Merging upstream version 126.0.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

140 files changed, 3734 insertions, 1989 deletions

diff --git a/servo/components/selectors/attr.rs b/servo/components/selectors/attr.rs
index fee2962237..70a0c5ea95 100644
--- a/servo/components/selectors/attr.rs
+++ b/servo/components/selectors/attr.rs
@@ -111,16 +111,21 @@ impl AttrSelectorOperator {
         let case = case_sensitivity;
         match self {
             AttrSelectorOperator::Equal => case.eq(e, s),
-            AttrSelectorOperator::Prefix => e.len() >= s.len() && case.eq(&e[..s.len()], s),
+            AttrSelectorOperator::Prefix => {
+                !s.is_empty() && e.len() >= s.len() && case.eq(&e[..s.len()], s)
+            },
             AttrSelectorOperator::Suffix => {
-                e.len() >= s.len() && case.eq(&e[(e.len() - s.len())..], s)
+                !s.is_empty() && e.len() >= s.len() && case.eq(&e[(e.len() - s.len())..], s)
             },
             AttrSelectorOperator::Substring => {
-                case.contains(element_attr_value, attr_selector_value)
+                !s.is_empty() && case.contains(element_attr_value, attr_selector_value)
+            },
+            AttrSelectorOperator::Includes => {
+                !s.is_empty() &&
+                    element_attr_value
+                        .split(SELECTOR_WHITESPACE)
+                        .any(|part| case.eq(part.as_bytes(), s))
             },
-            AttrSelectorOperator::Includes => element_attr_value
-                .split(SELECTOR_WHITESPACE)
-                .any(|part| case.eq(part.as_bytes(), s)),
             AttrSelectorOperator::DashMatch => {
                 case.eq(e, s) || (e.get(s.len()) == Some(&b'-') && case.eq(&e[..s.len()], s))
             },
diff --git a/servo/components/selectors/builder.rs b/servo/components/selectors/builder.rs
index 2406cd84f6..c706554185 100644
--- a/servo/components/selectors/builder.rs
+++ b/servo/components/selectors/builder.rs
@@ -6,59 +6,45 @@
 //!
 //! Our selector representation is designed to optimize matching, and has
 //! several requirements:
-//! * All simple selectors and combinators are stored inline in the same buffer
-//!   as Component instances.
-//! * We store the top-level compound selectors from right to left, i.e. in
-//!   matching order.
-//! * We store the simple selectors for each combinator from left to right, so
-//!   that we match the cheaper simple selectors first.
+//! * All simple selectors and combinators are stored inline in the same buffer as Component
+//!   instances.
+//! * We store the top-level compound selectors from right to left, i.e. in matching order.
+//! * We store the simple selectors for each combinator from left to right, so that we match the
+//!   cheaper simple selectors first.
 //!
-//! Meeting all these constraints without extra memmove traffic during parsing
-//! is non-trivial. This module encapsulates those details and presents an
-//! easy-to-use API for the parser.
+//! For example, the selector:
+//!
+//!   .bar:hover > .baz:nth-child(2) + .qux
+//!
+//! Gets stored as:
+//!
+//!   [.qux,  + , .baz, :nth-child(2),  > , .bar, :hover]
+//!
+//! Meeting all these constraints without extra memmove traffic during parsing is non-trivial. This
+//! module encapsulates those details and presents an easy-to-use API for the parser.
 
-use crate::parser::{Combinator, Component, RelativeSelector, Selector, SelectorImpl};
+use crate::parser::{Combinator, Component, RelativeSelector, Selector, SelectorImpl, ParseRelative};
 use crate::sink::Push;
 use servo_arc::{Arc, ThinArc};
-use smallvec::{self, SmallVec};
+use smallvec::SmallVec;
 use std::cmp;
-use std::iter;
-use std::ptr;
 use std::slice;
 
-/// Top-level SelectorBuilder struct. This should be stack-allocated by the
-/// consumer and never moved (because it contains a lot of inline data that
-/// would be slow to memmov).
+/// Top-level SelectorBuilder struct. This should be stack-allocated by the consumer and never
+/// moved (because it contains a lot of inline data that would be slow to memmove).
 ///
-/// After instantation, callers may call the push_simple_selector() and
-/// push_combinator() methods to append selector data as it is encountered
-/// (from left to right). Once the process is complete, callers should invoke
-/// build(), which transforms the contents of the SelectorBuilder into a heap-
-/// allocated Selector and leaves the builder in a drained state.
+/// After instantiation, callers may call the push_simple_selector() and push_combinator() methods
+/// to append selector data as it is encountered (from left to right). Once the process is
+/// complete, callers should invoke build(), which transforms the contents of the SelectorBuilder
+/// into a heap- allocated Selector and leaves the builder in a drained state.
 #[derive(Debug)]
 pub struct SelectorBuilder<Impl: SelectorImpl> {
-    /// The entire sequence of simple selectors, from left to right, without combinators.
-    ///
-    /// We make this large because the result of parsing a selector is fed into a new
-    /// Arc-ed allocation, so any spilled vec would be a wasted allocation. Also,
-    /// Components are large enough that we don't have much cache locality benefit
-    /// from reserving stack space for fewer of them.
-    simple_selectors: SmallVec<[Component<Impl>; 32]>,
-    /// The combinators, and the length of the compound selector to their left.
-    combinators: SmallVec<[(Combinator, usize); 16]>,
-    /// The length of the current compount selector.
-    current_len: usize,
-}
-
-impl<Impl: SelectorImpl> Default for SelectorBuilder<Impl> {
-    #[inline(always)]
-    fn default() -> Self {
-        SelectorBuilder {
-            simple_selectors: SmallVec::new(),
-            combinators: SmallVec::new(),
-            current_len: 0,
-        }
-    }
+    /// The entire sequence of components. We make this large because the result of parsing a
+    /// selector is fed into a new Arc-ed allocation, so any spilled vec would be a wasted
+    /// allocation. Also, Components are large enough that we don't have much cache locality
+    /// benefit from reserving stack space for fewer of them.
+    components: SmallVec<[Component<Impl>; 32]>,
+    last_compound_start: Option<usize>,
 }
 
 impl<Impl: SelectorImpl> Push<Component<Impl>> for SelectorBuilder<Impl> {
@@ -71,101 +57,115 @@ impl<Impl: SelectorImpl> SelectorBuilder<Impl> {
     /// Pushes a simple selector onto the current compound selector.
     #[inline(always)]
     pub fn push_simple_selector(&mut self, ss: Component<Impl>) {
-        assert!(!ss.is_combinator());
-        self.simple_selectors.push(ss);
-        self.current_len += 1;
+        debug_assert!(!ss.is_combinator());
+        self.components.push(ss);
     }
 
-    /// Completes the current compound selector and starts a new one, delimited
-    /// by the given combinator.
+    /// Completes the current compound selector and starts a new one, delimited by the given
+    /// combinator.
     #[inline(always)]
     pub fn push_combinator(&mut self, c: Combinator) {
-        self.combinators.push((c, self.current_len));
-        self.current_len = 0;
+        self.reverse_last_compound();
+        self.components.push(Component::Combinator(c));
+        self.last_compound_start = Some(self.components.len());
+    }
+
+    fn reverse_last_compound(&mut self) {
+        let start = self.last_compound_start.unwrap_or(0);
+        self.components[start..].reverse();
     }
 
     /// Returns true if combinators have ever been pushed to this builder.
     #[inline(always)]
     pub fn has_combinators(&self) -> bool {
-        !self.combinators.is_empty()
+        self.last_compound_start.is_some()
     }
 
     /// Consumes the builder, producing a Selector.
     #[inline(always)]
-    pub fn build(&mut self) -> ThinArc<SpecificityAndFlags, Component<Impl>> {
+    pub fn build(&mut self, parse_relative: ParseRelative) -> ThinArc<SpecificityAndFlags, Component<Impl>> {
         // Compute the specificity and flags.
-        let sf = specificity_and_flags(self.simple_selectors.iter());
-        self.build_with_specificity_and_flags(sf)
+        let sf = specificity_and_flags(self.components.iter());
+        self.build_with_specificity_and_flags(sf, parse_relative)
     }
 
-    /// Builds with an explicit SpecificityAndFlags. This is separated from build() so
-    /// that unit tests can pass an explicit specificity.
+    /// Builds with an explicit SpecificityAndFlags. This is separated from build() so that unit
+    /// tests can pass an explicit specificity.
     #[inline(always)]
     pub(crate) fn build_with_specificity_and_flags(
         &mut self,
-        spec: SpecificityAndFlags,
+        mut spec: SpecificityAndFlags,
+        parse_relative: ParseRelative,
     ) -> ThinArc<SpecificityAndFlags, Component<Impl>> {
-        // Create the Arc using an iterator that drains our buffers.
-        // Panic-safety: if SelectorBuilderIter is not iterated to the end, some simple selectors
-        // will safely leak.
-        let raw_simple_selectors = unsafe {
-            let simple_selectors_len = self.simple_selectors.len();
-            self.simple_selectors.set_len(0);
-            std::slice::from_raw_parts(self.simple_selectors.as_ptr(), simple_selectors_len)
-        };
-        let (rest, current) = split_from_end(raw_simple_selectors, self.current_len);
-        let iter = SelectorBuilderIter {
-            current_simple_selectors: current.iter(),
-            rest_of_simple_selectors: rest,
-            combinators: self.combinators.drain(..).rev(),
+        let implicit_parent = parse_relative.needs_implicit_parent_selector() &&
+            !spec.flags.contains(SelectorFlags::HAS_PARENT);
+
+        let parent_selector_and_combinator;
+        let implicit_parent = if implicit_parent {
+            spec.flags.insert(SelectorFlags::HAS_PARENT);
+            parent_selector_and_combinator = [
+                Component::Combinator(Combinator::Descendant),
+                Component::ParentSelector,
+            ];
+            &parent_selector_and_combinator[..]
+        } else {
+            &[]
         };
 
-        Arc::from_header_and_iter(spec, iter)
+        // As an optimization, for a selector without combinators, we can just keep the order
+        // as-is.
+        if self.last_compound_start.is_none() {
+            return Arc::from_header_and_iter(spec, ExactChain(self.components.drain(..), implicit_parent.iter().cloned()));
+        }
+
+        self.reverse_last_compound();
+        Arc::from_header_and_iter(spec, ExactChain(self.components.drain(..).rev(), implicit_parent.iter().cloned()))
     }
 }
 
-struct SelectorBuilderIter<'a, Impl: SelectorImpl> {
-    current_simple_selectors: slice::Iter<'a, Component<Impl>>,
-    rest_of_simple_selectors: &'a [Component<Impl>],
-    combinators: iter::Rev<smallvec::Drain<'a, [(Combinator, usize); 16]>>,
+
+impl<Impl: SelectorImpl> Default for SelectorBuilder<Impl> {
+    #[inline(always)]
+    fn default() -> Self {
+        SelectorBuilder {
+            components: SmallVec::new(),
+            last_compound_start: None,
+        }
+    }
 }
 
-impl<'a, Impl: SelectorImpl> ExactSizeIterator for SelectorBuilderIter<'a, Impl> {
+// This is effectively a Chain<>, but Chain isn't an ExactSizeIterator, see
+// https://github.com/rust-lang/rust/issues/34433
+struct ExactChain<A, B>(A, B);
+
+impl<A, B, Item> ExactSizeIterator for ExactChain<A, B>
+where
+    A: ExactSizeIterator<Item = Item>,
+    B: ExactSizeIterator<Item = Item>,
+{
     fn len(&self) -> usize {
-        self.current_simple_selectors.len() +
-            self.rest_of_simple_selectors.len() +
-            self.combinators.len()
+        self.0.len() + self.1.len()
     }
 }
 
-impl<'a, Impl: SelectorImpl> Iterator for SelectorBuilderIter<'a, Impl> {
-    type Item = Component<Impl>;
+impl<A, B, Item> Iterator for ExactChain<A, B>
+where
+    A: ExactSizeIterator<Item = Item>,
+    B: ExactSizeIterator<Item = Item>,
+{
+    type Item = Item;
+
     #[inline(always)]
     fn next(&mut self) -> Option<Self::Item> {
-        if let Some(simple_selector_ref) = self.current_simple_selectors.next() {
-            // Move a simple selector out of this slice iterator.
-            // This is safe because we’ve called SmallVec::set_len(0) above,
-            // so SmallVec::drop won’t drop this simple selector.
-            unsafe { Some(ptr::read(simple_selector_ref)) }
-        } else {
-            self.combinators.next().map(|(combinator, len)| {
-                let (rest, current) = split_from_end(self.rest_of_simple_selectors, len);
-                self.rest_of_simple_selectors = rest;
-                self.current_simple_selectors = current.iter();
-                Component::Combinator(combinator)
-            })
-        }
+        self.0.next().or_else(|| self.1.next())
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        (self.len(), Some(self.len()))
+        let len = self.len();
+        (len, Some(len))
     }
 }
 
-fn split_from_end<T>(s: &[T], at: usize) -> (&[T], &[T]) {
-    s.split_at(s.len() - at)
-}
-
 /// Flags that indicate at which point of parsing a selector are we.
 #[derive(Clone, Copy, Default, Eq, PartialEq, ToShmem)]
 pub(crate) struct SelectorFlags(u8);
diff --git a/servo/components/selectors/context.rs b/servo/components/selectors/context.rs
index 84ee262dfe..289b081b64 100644
--- a/servo/components/selectors/context.rs
+++ b/servo/components/selectors/context.rs
@@ -79,10 +79,18 @@ pub enum NeedsSelectorFlags {
 }
 
 /// Whether we're matching in the contect of invalidation.
-#[derive(PartialEq)]
+#[derive(Clone, Copy, PartialEq)]
 pub enum MatchingForInvalidation {
     No,
     Yes,
+    YesForComparison,
+}
+
+impl MatchingForInvalidation {
+    /// Are we matching for invalidation?
+    pub fn is_for_invalidation(&self) -> bool {
+        matches!(*self, Self::Yes | Self::YesForComparison)
+    }
 }
 
 /// Which quirks mode is this document in.
@@ -314,7 +322,31 @@ where
     /// Whether or not we're matching to invalidate.
     #[inline]
     pub fn matching_for_invalidation(&self) -> bool {
-        self.matching_for_invalidation == MatchingForInvalidation::Yes
+        self.matching_for_invalidation.is_for_invalidation()
+    }
+
+    /// Whether or not we're comparing for invalidation, if we are matching for invalidation.
+    #[inline]
+    pub fn matching_for_invalidation_comparison(&self) -> Option<bool> {
+        match self.matching_for_invalidation {
+            MatchingForInvalidation::No => None,
+            MatchingForInvalidation::Yes => Some(false),
+            MatchingForInvalidation::YesForComparison => Some(true),
+        }
+    }
+
+    /// Run the given matching function for before/after invalidation comparison.
+    #[inline]
+    pub fn for_invalidation_comparison<F, R>(&mut self, f: F) -> R
+    where
+        F: FnOnce(&mut Self) -> R,
+    {
+        debug_assert!(self.matching_for_invalidation(), "Not matching for invalidation?");
+        let prev = self.matching_for_invalidation;
+        self.matching_for_invalidation = MatchingForInvalidation::YesForComparison;
+        let result = f(self);
+        self.matching_for_invalidation = prev;
+        result
     }
 
     /// The case-sensitivity for class and ID selectors
diff --git a/servo/components/selectors/kleene_value.rs b/servo/components/selectors/kleene_value.rs
new file mode 100644
index 0000000000..58141c1156
--- /dev/null
+++ b/servo/components/selectors/kleene_value.rs
@@ -0,0 +1,131 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Kleen logic: https://en.wikipedia.org/wiki/Three-valued_logic#Kleene_and_Priest_logics
+
+/// A "trilean" value based on Kleen logic.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum KleeneValue {
+    /// False
+    False = 0,
+    /// True
+    True = 1,
+    /// Either true or false, but we’re not sure which yet.
+    Unknown,
+}
+
+impl From<bool> for KleeneValue {
+    fn from(b: bool) -> Self {
+        if b {
+            Self::True
+        } else {
+            Self::False
+        }
+    }
+}
+
+impl KleeneValue {
+    /// Turns this Kleene value to a bool, taking the unknown value as an
+    /// argument.
+    pub fn to_bool(self, unknown: bool) -> bool {
+        match self {
+            Self::True => true,
+            Self::False => false,
+            Self::Unknown => unknown,
+        }
+    }
+
+    /// Return true if any result of f() is true. Otherwise, return the strongest value seen.
+    /// Returns false if empty, like that of `Iterator`.
+    pub fn any<T>(
+        iter: impl Iterator<Item = T>,
+        f: impl FnMut(T) -> Self,
+    ) -> Self {
+        Self::any_value(iter, Self::True, Self::False, f)
+    }
+
+    /// Return false if any results of f() is false. Otherwise, return the strongest value seen.
+    /// Returns true if empty, opposite of `Iterator`.
+    pub fn any_false<T>(
+        iter: impl Iterator<Item = T>,
+        f: impl FnMut(T) -> Self,
+    ) -> Self {
+        Self::any_value(iter, Self::False, Self::True, f)
+    }
+
+    fn any_value<T>(
+        iter: impl Iterator<Item = T>,
+        value: Self,
+        on_empty: Self,
+        mut f: impl FnMut(T) -> Self,
+    ) -> Self {
+        let mut result = None;
+        for item in iter {
+            let r = f(item);
+            if r == value {
+                return r;
+            }
+            if let Some(v) = result.as_mut() {
+                *v = *v & r;
+            } else {
+                result = Some(r);
+            }
+        }
+        result.unwrap_or(on_empty)
+    }
+}
+
+impl std::ops::Not for KleeneValue {
+    type Output = Self;
+
+    fn not(self) -> Self {
+        match self {
+            Self::True => Self::False,
+            Self::False => Self::True,
+            Self::Unknown => Self::Unknown,
+        }
+    }
+}
+
+// Implements the logical and operation.
+impl std::ops::BitAnd for KleeneValue {
+    type Output = Self;
+
+    fn bitand(self, other: Self) -> Self {
+        if self == Self::False || other == Self::False {
+            return Self::False;
+        }
+        if self == Self::Unknown || other == Self::Unknown {
+            return Self::Unknown;
+        }
+        Self::True
+    }
+}
+
+// Implements the logical or operation.
+impl std::ops::BitOr for KleeneValue {
+    type Output = Self;
+
+    fn bitor(self, other: Self) -> Self {
+        if self == Self::True || other == Self::True {
+            return Self::True;
+        }
+        if self == Self::Unknown || other == Self::Unknown {
+            return Self::Unknown;
+        }
+        Self::False
+    }
+}
+
+impl std::ops::BitOrAssign for KleeneValue {
+    fn bitor_assign(&mut self, other: Self) {
+        *self = *self | other;
+    }
+}
+
+impl std::ops::BitAndAssign for KleeneValue {
+    fn bitand_assign(&mut self, other: Self) {
+        *self = *self & other;
+    }
+}
diff --git a/servo/components/selectors/lib.rs b/servo/components/selectors/lib.rs
index d909059ccf..6e300893d2 100644
--- a/servo/components/selectors/lib.rs
+++ b/servo/components/selectors/lib.rs
@@ -35,6 +35,7 @@ pub mod relative_selector;
 pub mod sink;
 mod tree;
 pub mod visitor;
+pub mod kleene_value;
 
 pub use crate::nth_index_cache::NthIndexCache;
 pub use crate::parser::{Parser, SelectorImpl, SelectorList};
diff --git a/servo/components/selectors/matching.rs b/servo/components/selectors/matching.rs
index 763f65d547..282d04064b 100644
--- a/servo/components/selectors/matching.rs
+++ b/servo/components/selectors/matching.rs
@@ -7,6 +7,7 @@ use crate::attr::{
     ParsedAttrSelectorOperation, ParsedCaseSensitivity,
 };
 use crate::bloom::{BloomFilter, BLOOM_HASH_MASK};
+use crate::kleene_value::KleeneValue;
 use crate::parser::{
     AncestorHashes, Combinator, Component, LocalName, NthSelectorData, RelativeSelectorMatchHint,
 };
@@ -200,12 +201,39 @@ fn may_match(hashes: &AncestorHashes, bf: &BloomFilter) -> bool {
 /// However since the selector "c1" raises
 /// NotMatchedAndRestartFromClosestDescendant. So the selector
 /// "b1 + c1 > b2 ~ " doesn't match and restart matching from "d1".
+///
+/// There is also the unknown result, which is used during invalidation when
+/// specific selector is being tested for before/after comparison. More specifically,
+/// selectors that are too expensive to correctly compute during invalidation may
+/// return unknown, as the computation will be thrown away and only to be recomputed
+/// during styling. For most cases, the unknown result can be treated as matching.
+/// This is because a compound of selectors acts like &&, and unknown && matched
+/// == matched and unknown && not-matched == not-matched. However, some selectors,
+/// like `:is()`, behave like || i.e. `:is(.a, .b)` == a || b. Treating unknown
+/// == matching then causes these selectors to always return matching, which undesired
+/// for before/after comparison. Coercing to not-matched doesn't work since each
+/// inner selector may have compounds: e.g. Toggling `.foo` in `:is(.foo:has(..))`
+/// with coersion to not-matched would result in an invalid before/after comparison
+/// of not-matched/not-matched.
 #[derive(Clone, Copy, Eq, PartialEq)]
 enum SelectorMatchingResult {
     Matched,
     NotMatchedAndRestartFromClosestLaterSibling,
     NotMatchedAndRestartFromClosestDescendant,
     NotMatchedGlobally,
+    Unknown,
+}
+
+impl From<SelectorMatchingResult> for KleeneValue {
+    fn from(value: SelectorMatchingResult) -> Self {
+        match value {
+            SelectorMatchingResult::Matched => KleeneValue::True,
+            SelectorMatchingResult::Unknown => KleeneValue::Unknown,
+            SelectorMatchingResult::NotMatchedAndRestartFromClosestLaterSibling |
+            SelectorMatchingResult::NotMatchedAndRestartFromClosestDescendant |
+            SelectorMatchingResult::NotMatchedGlobally => KleeneValue::False,
+        }
+    }
 }
 
 /// Matches a selector, fast-rejecting against a bloom filter.
@@ -227,11 +255,33 @@ pub fn matches_selector<E>(
 where
     E: Element,
 {
+    let result = matches_selector_kleene(selector, offset, hashes, element, context);
+    if cfg!(debug_assertions) && result == KleeneValue::Unknown {
+        debug_assert!(
+            context.matching_for_invalidation_comparison().unwrap_or(false),
+            "How did we return unknown?"
+        );
+    }
+    result.to_bool(true)
+}
+
+/// Same as matches_selector, but returns the Kleene value as-is.
+#[inline(always)]
+pub fn matches_selector_kleene<E>(
+    selector: &Selector<E::Impl>,
+    offset: usize,
+    hashes: Option<&AncestorHashes>,
+    element: &E,
+    context: &mut MatchingContext<E::Impl>,
+) -> KleeneValue
+where
+    E: Element,
+{
     // Use the bloom filter to fast-reject.
     if let Some(hashes) = hashes {
         if let Some(filter) = context.bloom_filter {
             if !may_match(hashes, filter) {
-                return false;
+                return KleeneValue::False;
             }
         }
     }
@@ -275,6 +325,12 @@ pub fn matches_compound_selector_from<E>(
 where
     E: Element,
 {
+    debug_assert!(
+        !context
+            .matching_for_invalidation_comparison()
+            .unwrap_or(false),
+        "CompoundSelectorMatchingResult doesn't support unknown"
+    );
     if cfg!(debug_assertions) && from_offset != 0 {
         selector.combinator_at_parse_order(from_offset - 1); // This asserts.
     }
@@ -320,7 +376,9 @@ where
     );
 
     for component in iter {
-        if !matches_simple_selector(component, element, &mut local_context) {
+        let result = matches_simple_selector(component, element, &mut local_context);
+        debug_assert!(result != KleeneValue::Unknown, "Returned unknown in non invalidation context?");
+        if !result.to_bool(true) {
             return CompoundSelectorMatchingResult::NotMatched;
         }
     }
@@ -341,7 +399,7 @@ fn matches_complex_selector<E>(
     element: &E,
     context: &mut MatchingContext<E::Impl>,
     rightmost: SubjectOrPseudoElement,
-) -> bool
+) -> KleeneValue
 where
     E: Element,
 {
@@ -353,7 +411,7 @@ where
             Component::PseudoElement(ref pseudo) => {
                 if let Some(ref f) = context.pseudo_element_matching_fn {
                     if !f(pseudo) {
-                        return false;
+                        return KleeneValue::False;
                     }
                 }
             },
@@ -364,12 +422,12 @@ where
                      in a non-pseudo selector {:?}",
                     other
                 );
-                return false;
+                return KleeneValue::False;
             },
         }
 
         if !iter.matches_for_stateless_pseudo_element() {
-            return false;
+            return KleeneValue::False;
         }
 
         // Advance to the non-pseudo-element part of the selector.
@@ -377,9 +435,14 @@ where
         debug_assert_eq!(next_sequence, Combinator::PseudoElement);
     }
 
-    let result = matches_complex_selector_internal(iter, element, context, rightmost);
-
-    matches!(result, SelectorMatchingResult::Matched)
+    matches_complex_selector_internal(
+        iter,
+        element,
+        context,
+        rightmost,
+        SubjectOrPseudoElement::Yes,
+    )
+    .into()
 }
 
 /// Matches each selector of a list as a complex selector
@@ -388,13 +451,16 @@ fn matches_complex_selector_list<E: Element>(
     element: &E,
     context: &mut MatchingContext<E::Impl>,
     rightmost: SubjectOrPseudoElement,
-) -> bool {
-    for selector in list {
-        if matches_complex_selector(selector.iter(), element, context, rightmost) {
-            return true;
-        }
-    }
-    false
+) -> KleeneValue {
+    KleeneValue::any(
+        list.iter(),
+        |selector| matches_complex_selector(
+            selector.iter(),
+            element,
+            context,
+            rightmost
+        )
+    )
 }
 
 fn matches_relative_selector<E: Element>(
@@ -423,7 +489,8 @@ fn matches_relative_selector<E: Element>(
                 &el,
                 context,
                 rightmost,
-            );
+            )
+            .to_bool(true);
             if !matched && relative_selector.match_hint.is_subtree() {
                 matched = matches_relative_selector_subtree(
                     &relative_selector.selector,
@@ -472,6 +539,7 @@ fn matches_relative_selector<E: Element>(
                 )
             } else {
                 matches_complex_selector(relative_selector.selector.iter(), &el, context, rightmost)
+                    .to_bool(true)
             };
             if matched {
                 return true;
@@ -490,12 +558,6 @@ fn relative_selector_match_early<E: Element>(
     element: &E,
     context: &mut MatchingContext<E::Impl>,
 ) -> Option<bool> {
-    if context.matching_for_invalidation() {
-        // In the context of invalidation, we can't use caching/filtering due to
-        // now/then matches. DOM structure also may have changed, so just pretend
-        // that we always match.
-        return Some(!context.in_negation());
-    }
     // See if we can return a cached result.
     if let Some(cached) = context
         .selector_caches
@@ -526,18 +588,28 @@ fn match_relative_selectors<E: Element>(
     element: &E,
     context: &mut MatchingContext<E::Impl>,
     rightmost: SubjectOrPseudoElement,
-) -> bool {
+) -> KleeneValue {
     if context.relative_selector_anchor().is_some() {
         // FIXME(emilio): This currently can happen with nesting, and it's not fully
         // correct, arguably. But the ideal solution isn't super-clear either. For now,
         // cope with it and explicitly reject it at match time. See [1] for discussion.
         //
         // [1]: https://github.com/w3c/csswg-drafts/issues/9600
-        return false;
+        return KleeneValue::False;
+    }
+    if let Some(may_return_unknown) = context.matching_for_invalidation_comparison() {
+        // In the context of invalidation, :has is expensive, especially because we
+        // can't use caching/filtering due to now/then matches. DOM structure also
+        // may have changed.
+        return if may_return_unknown {
+            KleeneValue::Unknown
+        } else {
+            KleeneValue::from(!context.in_negation())
+        };
     }
     context.nest_for_relative_selector(element.opaque(), |context| {
         do_match_relative_selectors(selectors, element, context, rightmost)
-    })
+    }).into()
 }
 
 /// Matches a relative selector in a list of relative selectors.
@@ -604,7 +676,7 @@ fn matches_relative_selector_subtree<E: Element>(
                 ElementSelectorFlags::RELATIVE_SELECTOR_SEARCH_DIRECTION_ANCESTOR,
             );
         }
-        if matches_complex_selector(selector.iter(), &el, context, rightmost) {
+        if matches_complex_selector(selector.iter(), &el, context, rightmost).to_bool(true) {
             return true;
         }
 
@@ -643,19 +715,8 @@ fn hover_and_active_quirk_applies<Impl: SelectorImpl>(
     }
 
     selector_iter.clone().all(|simple| match *simple {
-        Component::LocalName(_) |
-        Component::AttributeInNoNamespaceExists { .. } |
-        Component::AttributeInNoNamespace { .. } |
-        Component::AttributeOther(_) |
-        Component::ID(_) |
-        Component::Class(_) |
-        Component::PseudoElement(_) |
-        Component::Negation(_) |
-        Component::Empty |
-        Component::Nth(_) |
-        Component::NthOf(_) => false,
         Component::NonTSPseudoClass(ref pseudo_class) => pseudo_class.is_active_or_hover(),
-        _ => true,
+        _ => false,
     })
 }
 
@@ -753,6 +814,7 @@ fn matches_complex_selector_internal<E>(
     element: &E,
     context: &mut MatchingContext<E::Impl>,
     rightmost: SubjectOrPseudoElement,
+    first_subject_compound: SubjectOrPseudoElement,
 ) -> SelectorMatchingResult
 where
     E: Element,
@@ -762,8 +824,24 @@ where
         selector_iter, element
     );
 
-    let matches_compound_selector =
-        matches_compound_selector(&mut selector_iter, element, context, rightmost);
+    let matches_compound_selector = {
+        let result = matches_compound_selector(&mut selector_iter, element, context, rightmost);
+        // We only care for unknown match in the first subject in compound - in the context of comparison
+        // invalidation, ancestors/previous sibling being an unknown match doesn't matter - we must
+        // invalidate to guarantee correctness.
+        if result == KleeneValue::Unknown && first_subject_compound == SubjectOrPseudoElement::No {
+            debug_assert!(
+                context
+                    .matching_for_invalidation_comparison()
+                    .unwrap_or(false),
+                "How did we return unknown?"
+            );
+            // Coerce the result to matched.
+            KleeneValue::True
+        } else {
+            result
+        }
+    };
 
     let combinator = selector_iter.next_sequence();
     if combinator.map_or(false, |c| c.is_sibling()) {
@@ -772,24 +850,42 @@ where
         }
     }
 
-    if !matches_compound_selector {
+    // We don't short circuit unknown here, since the rest of the selector
+    // to the left of this compound may return false.
+    if matches_compound_selector == KleeneValue::False {
         return SelectorMatchingResult::NotMatchedAndRestartFromClosestLaterSibling;
     }
 
     let combinator = match combinator {
-        None => return SelectorMatchingResult::Matched,
+        None => {
+            return match matches_compound_selector {
+                KleeneValue::True => SelectorMatchingResult::Matched,
+                KleeneValue::Unknown => SelectorMatchingResult::Unknown,
+                KleeneValue::False => unreachable!(),
+            }
+        },
         Some(c) => c,
     };
 
-    let (candidate_not_found, mut rightmost) = match combinator {
-        Combinator::NextSibling | Combinator::LaterSibling => {
-            (SelectorMatchingResult::NotMatchedAndRestartFromClosestDescendant, SubjectOrPseudoElement::No)
-        },
+    let (candidate_not_found, rightmost, first_subject_compound) = match combinator {
+        Combinator::NextSibling | Combinator::LaterSibling => (
+            SelectorMatchingResult::NotMatchedAndRestartFromClosestDescendant,
+            SubjectOrPseudoElement::No,
+            SubjectOrPseudoElement::No,
+        ),
         Combinator::Child |
         Combinator::Descendant |
         Combinator::SlotAssignment |
-        Combinator::Part => (SelectorMatchingResult::NotMatchedGlobally, SubjectOrPseudoElement::No),
-        Combinator::PseudoElement => (SelectorMatchingResult::NotMatchedGlobally, rightmost),
+        Combinator::Part => (
+            SelectorMatchingResult::NotMatchedGlobally,
+            SubjectOrPseudoElement::No,
+            SubjectOrPseudoElement::No,
+        ),
+        Combinator::PseudoElement => (
+            SelectorMatchingResult::NotMatchedGlobally,
+            rightmost,
+            first_subject_compound,
+        ),
     };
 
     // Stop matching :visited as soon as we find a link, or a combinator for
@@ -818,18 +914,27 @@ where
                 &element,
                 context,
                 rightmost,
+                first_subject_compound,
             )
         });
 
-        if !matches!(combinator, Combinator::PseudoElement) {
-            rightmost = SubjectOrPseudoElement::No;
-        }
-
         match (result, combinator) {
             // Return the status immediately.
-            (SelectorMatchingResult::Matched, _) |
-            (SelectorMatchingResult::NotMatchedGlobally, _) |
-            (_, Combinator::NextSibling) => {
+            (SelectorMatchingResult::Matched | SelectorMatchingResult::Unknown, _) => {
+                debug_assert!(
+                    matches_compound_selector.to_bool(true),
+                    "Compound didn't match?"
+                );
+                if result == SelectorMatchingResult::Matched &&
+                    matches_compound_selector.to_bool(false)
+                {
+                    // Matches without question
+                    return result;
+                }
+                // Something returned unknown, so return unknown.
+                return SelectorMatchingResult::Unknown;
+            },
+            (SelectorMatchingResult::NotMatchedGlobally, _) | (_, Combinator::NextSibling) => {
                 return result;
             },
 
@@ -921,18 +1026,18 @@ fn matches_host<E>(
     selector: Option<&Selector<E::Impl>>,
     context: &mut MatchingContext<E::Impl>,
     rightmost: SubjectOrPseudoElement,
-) -> bool
+) -> KleeneValue
 where
     E: Element,
 {
     let host = match context.shadow_host() {
         Some(h) => h,
-        None => return false,
+        None => return KleeneValue::False,
     };
     if host != element.opaque() {
-        return false;
+        return KleeneValue::False;
     }
-    selector.map_or(true, |selector| {
+    selector.map_or(KleeneValue::True, |selector| {
         context
             .nest(|context| matches_complex_selector(selector.iter(), element, context, rightmost))
     })
@@ -943,13 +1048,13 @@ fn matches_slotted<E>(
     selector: &Selector<E::Impl>,
     context: &mut MatchingContext<E::Impl>,
     rightmost: SubjectOrPseudoElement,
-) -> bool
+) -> KleeneValue
 where
     E: Element,
 {
     // <slots> are never flattened tree slottables.
     if element.is_html_slot_element() {
-        return false;
+        return KleeneValue::False;
     }
     context.nest(|context| matches_complex_selector(selector.iter(), element, context, rightmost))
 }
@@ -994,7 +1099,7 @@ fn matches_compound_selector<E>(
     element: &E,
     context: &mut MatchingContext<E::Impl>,
     rightmost: SubjectOrPseudoElement,
-) -> bool
+) -> KleeneValue
 where
     E: Element,
 {
@@ -1008,7 +1113,14 @@ where
         rightmost,
         quirks_data,
     };
-    selector_iter.all(|simple| matches_simple_selector(simple, element, &mut local_context))
+    KleeneValue::any_false(
+        selector_iter,
+        |simple| matches_simple_selector(
+            simple,
+            element,
+            &mut local_context
+        )
+    )
 }
 
 /// Determines whether the given element matches the given single selector.
@@ -1016,13 +1128,13 @@ fn matches_simple_selector<E>(
     selector: &Component<E::Impl>,
     element: &E,
     context: &mut LocalMatchingContext<E::Impl>,
-) -> bool
+) -> KleeneValue
 where
     E: Element,
 {
     debug_assert!(context.shared.is_nested() || !context.shared.in_negation());
     let rightmost = context.rightmost;
-    match *selector {
+    KleeneValue::from(match *selector {
         Component::ID(ref id) => {
             element.has_id(id, context.shared.classes_and_ids_case_sensitivity())
         },
@@ -1053,7 +1165,7 @@ where
         },
         Component::Part(ref parts) => matches_part(element, parts, &mut context.shared),
         Component::Slotted(ref selector) => {
-            matches_slotted(element, selector, &mut context.shared, rightmost)
+            return matches_slotted(element, selector, &mut context.shared, rightmost);
         },
         Component::PseudoElement(ref pseudo) => {
             element.match_pseudo_element(pseudo, context.shared)
@@ -1072,7 +1184,7 @@ where
                     !element.is_link() &&
                     hover_and_active_quirk_applies(iter, context.shared, context.rightmost)
                 {
-                    return false;
+                    return KleeneValue::False;
                 }
             }
             element.match_non_ts_pseudo_class(pc, &mut context.shared)
@@ -1085,32 +1197,43 @@ where
             element.is_empty()
         },
         Component::Host(ref selector) => {
-            matches_host(element, selector.as_ref(), &mut context.shared, rightmost)
+            return matches_host(element, selector.as_ref(), &mut context.shared, rightmost);
         },
         Component::ParentSelector | Component::Scope => match context.shared.scope_element {
             Some(ref scope_element) => element.opaque() == *scope_element,
             None => element.is_root(),
         },
         Component::Nth(ref nth_data) => {
-            matches_generic_nth_child(element, context.shared, nth_data, &[], rightmost)
+            return matches_generic_nth_child(element, context.shared, nth_data, &[], rightmost);
         },
-        Component::NthOf(ref nth_of_data) => context.shared.nest(|context| {
-            matches_generic_nth_child(
+        Component::NthOf(ref nth_of_data) => {
+            return context.shared.nest(|context| {
+                matches_generic_nth_child(
+                    element,
+                    context,
+                    nth_of_data.nth_data(),
+                    nth_of_data.selectors(),
+                    rightmost,
+                )
+            })
+        },
+        Component::Is(ref list) | Component::Where(ref list) => {
+            return context.shared.nest(|context| {
+                matches_complex_selector_list(list.slice(), element, context, rightmost)
+            })
+        },
+        Component::Negation(ref list) => {
+            return context.shared.nest_for_negation(|context| {
+                !matches_complex_selector_list(list.slice(), element, context, rightmost)
+            })
+        },
+        Component::Has(ref relative_selectors) => {
+            return match_relative_selectors(
+                relative_selectors,
                 element,
-                context,
-                nth_of_data.nth_data(),
-                nth_of_data.selectors(),
+                context.shared,
                 rightmost,
-            )
-        }),
-        Component::Is(ref list) | Component::Where(ref list) => context.shared.nest(|context| {
-            matches_complex_selector_list(list.slice(), element, context, rightmost)
-        }),
-        Component::Negation(ref list) => context.shared.nest_for_negation(|context| {
-            !matches_complex_selector_list(list.slice(), element, context, rightmost)
-        }),
-        Component::Has(ref relative_selectors) => {
-            match_relative_selectors(relative_selectors, element, context.shared, rightmost)
+            );
         },
         Component::Combinator(_) => unsafe {
             debug_unreachable!("Shouldn't try to selector-match combinators")
@@ -1121,7 +1244,7 @@ where
             anchor.map_or(true, |a| a == element.opaque())
         },
         Component::Invalid(..) => false,
-    }
+    })
 }
 
 #[inline(always)]
@@ -1163,19 +1286,23 @@ fn matches_generic_nth_child<E>(
     nth_data: &NthSelectorData,
     selectors: &[Selector<E::Impl>],
     rightmost: SubjectOrPseudoElement,
-) -> bool
+) -> KleeneValue
 where
     E: Element,
 {
     if element.ignores_nth_child_selectors() {
-        return false;
+        return KleeneValue::False;
     }
     let has_selectors = !selectors.is_empty();
-    let selectors_match =
-        !has_selectors || matches_complex_selector_list(selectors, element, context, rightmost);
-    if context.matching_for_invalidation() {
+    let selectors_match = !has_selectors ||
+        matches_complex_selector_list(selectors, element, context, rightmost).to_bool(true);
+    if let Some(may_return_unknown) = context.matching_for_invalidation_comparison() {
         // Skip expensive indexing math in invalidation.
-        return selectors_match && !context.in_negation();
+        return if selectors_match && may_return_unknown {
+            KleeneValue::Unknown
+        } else {
+            KleeneValue::from(selectors_match && !context.in_negation())
+        };
     }
 
     let NthSelectorData { ty, a, b, .. } = *nth_data;
@@ -1185,18 +1312,23 @@ where
             !has_selectors,
             ":only-child and :only-of-type cannot have a selector list!"
         );
-        return matches_generic_nth_child(
-            element,
-            context,
-            &NthSelectorData::first(is_of_type),
-            selectors,
-            rightmost,
-        ) && matches_generic_nth_child(
-            element,
-            context,
-            &NthSelectorData::last(is_of_type),
-            selectors,
-            rightmost,
+        return KleeneValue::from(
+            matches_generic_nth_child(
+                element,
+                context,
+                &NthSelectorData::first(is_of_type),
+                selectors,
+                rightmost,
+            )
+            .to_bool(true) &&
+                matches_generic_nth_child(
+                    element,
+                    context,
+                    &NthSelectorData::last(is_of_type),
+                    selectors,
+                    rightmost,
+                )
+                .to_bool(true),
         );
     }
 
@@ -1223,7 +1355,7 @@ where
     }
 
     if !selectors_match {
-        return false;
+        return KleeneValue::False;
     }
 
     // :first/last-child are rather trivial to match, don't bother with the
@@ -1234,7 +1366,8 @@ where
         } else {
             element.prev_sibling_element()
         }
-        .is_none();
+        .is_none()
+        .into();
     }
 
     // Lookup or compute the index.
@@ -1280,6 +1413,7 @@ where
             None /* a == 0 */ => an == 0,
         },
     }
+    .into()
 }
 
 #[inline]
@@ -1314,7 +1448,7 @@ where
             let matches = if is_of_type {
                 element.is_same_type(&curr)
             } else if !selectors.is_empty() {
-                matches_complex_selector_list(selectors, &curr, context, rightmost)
+                matches_complex_selector_list(selectors, &curr, context, rightmost).to_bool(true)
             } else {
                 true
             };
@@ -1345,7 +1479,7 @@ where
         let matches = if is_of_type {
             element.is_same_type(&curr)
         } else if !selectors.is_empty() {
-            matches_complex_selector_list(selectors, &curr, context, rightmost)
+            matches_complex_selector_list(selectors, &curr, context, rightmost).to_bool(true)
         } else {
             true
         };
diff --git a/servo/components/selectors/parser.rs b/servo/components/selectors/parser.rs
index 9b0acb0671..37b2b00ca5 100644
--- a/servo/components/selectors/parser.rs
+++ b/servo/components/selectors/parser.rs
@@ -438,10 +438,20 @@ pub enum ParseRelative {
     /// Allow selectors to start with a combinator, prepending a parent selector if so. Do nothing
     /// otherwise
     ForNesting,
+    /// Allow selectors to start with a combinator, prepending a scope selector if so. Do nothing
+    /// otherwise
+    ForScope,
     /// Treat as parse error if any selector begins with a combinator.
     No,
 }
 
+impl ParseRelative {
+    #[inline]
+    pub(crate) fn needs_implicit_parent_selector(self) -> bool {
+        matches!(self, Self::ForNesting)
+    }
+}
+
 impl<Impl: SelectorImpl> SelectorList<Impl> {
     /// Returns a selector list with a single `&`
     pub fn ampersand() -> Self {
@@ -469,6 +479,23 @@ impl<Impl: SelectorImpl> SelectorList<Impl> {
         )
     }
 
+    pub fn parse_forgiving<'i, 't, P>(
+        parser: &P,
+        input: &mut CssParser<'i, 't>,
+        parse_relative: ParseRelative,
+    ) -> Result<Self, ParseError<'i, P::Error>>
+    where
+        P: Parser<'i, Impl = Impl>,
+    {
+        Self::parse_with_state(
+            parser,
+            input,
+            SelectorParsingState::empty(),
+            ForgivingParsing::Yes,
+            parse_relative,
+        )
+    }
+
     #[inline]
     fn parse_with_state<'i, 't, P>(
         parser: &P,
@@ -932,7 +959,7 @@ impl<Impl: SelectorImpl> Selector<Impl> {
             }
         }
         let spec = SpecificityAndFlags { specificity, flags };
-        Selector(builder.build_with_specificity_and_flags(spec))
+        Selector(builder.build_with_specificity_and_flags(spec, ParseRelative::No))
     }
 
     #[inline]
@@ -960,9 +987,6 @@ impl<Impl: SelectorImpl> Selector<Impl> {
             }
 
             let result = SelectorList::from_iter(orig.iter().map(|s| {
-                if !s.has_parent_selector() {
-                    return s.clone();
-                }
                 s.replace_parent_selector(parent)
             }));
 
@@ -1030,82 +1054,53 @@ impl<Impl: SelectorImpl> Selector<Impl> {
             flags: &mut SelectorFlags,
             flags_to_propagate: SelectorFlags,
         ) -> Selector<Impl> {
-            if !orig.has_parent_selector() {
-                return orig.clone();
-            }
             let new_selector = orig.replace_parent_selector(parent);
             *specificity += Specificity::from(new_selector.specificity() - orig.specificity());
             flags.insert(new_selector.flags().intersection(flags_to_propagate));
             new_selector
         }
 
-        let mut items = if !self.has_parent_selector() {
-            // Implicit `&` plus descendant combinator.
-            let iter = self.iter_raw_match_order();
-            let len = iter.len() + 2;
-            specificity += Specificity::from(parent_specificity_and_flags.specificity);
-            flags.insert(
-                parent_specificity_and_flags
-                    .flags
-                    .intersection(SelectorFlags::for_nesting()),
-            );
-            let iter = iter
-                .cloned()
-                .chain(std::iter::once(Component::Combinator(
-                    Combinator::Descendant,
-                )))
-                .chain(std::iter::once(Component::Is(parent.clone())));
-            UniqueArc::from_header_and_iter_with_size(Default::default(), iter, len)
-        } else {
-            let iter = self.iter_raw_match_order().map(|component| {
-                use self::Component::*;
-                match *component {
-                    LocalName(..) |
-                    ID(..) |
-                    Class(..) |
-                    AttributeInNoNamespaceExists { .. } |
-                    AttributeInNoNamespace { .. } |
-                    AttributeOther(..) |
-                    ExplicitUniversalType |
-                    ExplicitAnyNamespace |
-                    ExplicitNoNamespace |
-                    DefaultNamespace(..) |
-                    Namespace(..) |
-                    Root |
-                    Empty |
-                    Scope |
-                    Nth(..) |
-                    NonTSPseudoClass(..) |
-                    PseudoElement(..) |
-                    Combinator(..) |
-                    Host(None) |
-                    Part(..) |
-                    Invalid(..) |
-                    RelativeSelectorAnchor => component.clone(),
-                    ParentSelector => {
-                        specificity += Specificity::from(parent_specificity_and_flags.specificity);
-                        flags.insert(
-                            parent_specificity_and_flags
-                                .flags
-                                .intersection(SelectorFlags::for_nesting()),
-                        );
-                        Is(parent.clone())
-                    },
-                    Negation(ref selectors) => {
-                        Negation(
-                            replace_parent_on_selector_list(
-                                selectors.slice(),
-                                parent,
-                                &mut specificity,
-                                &mut flags,
-                                /* propagate_specificity = */ true,
-                                SelectorFlags::for_nesting(),
-                            )
-                            .unwrap_or_else(|| selectors.clone()),
-                        )
-                    },
-                    Is(ref selectors) => {
-                        Is(replace_parent_on_selector_list(
+        if !self.has_parent_selector() {
+            return self.clone();
+        }
+
+        let iter = self.iter_raw_match_order().map(|component| {
+            use self::Component::*;
+            match *component {
+                LocalName(..) |
+                ID(..) |
+                Class(..) |
+                AttributeInNoNamespaceExists { .. } |
+                AttributeInNoNamespace { .. } |
+                AttributeOther(..) |
+                ExplicitUniversalType |
+                ExplicitAnyNamespace |
+                ExplicitNoNamespace |
+                DefaultNamespace(..) |
+                Namespace(..) |
+                Root |
+                Empty |
+                Scope |
+                Nth(..) |
+                NonTSPseudoClass(..) |
+                PseudoElement(..) |
+                Combinator(..) |
+                Host(None) |
+                Part(..) |
+                Invalid(..) |
+                RelativeSelectorAnchor => component.clone(),
+                ParentSelector => {
+                    specificity += Specificity::from(parent_specificity_and_flags.specificity);
+                    flags.insert(
+                        parent_specificity_and_flags
+                            .flags
+                            .intersection(SelectorFlags::for_nesting()),
+                    );
+                    Is(parent.clone())
+                },
+                Negation(ref selectors) => {
+                    Negation(
+                        replace_parent_on_selector_list(
                             selectors.slice(),
                             parent,
                             &mut specificity,
@@ -1113,64 +1108,75 @@ impl<Impl: SelectorImpl> Selector<Impl> {
                             /* propagate_specificity = */ true,
                             SelectorFlags::for_nesting(),
                         )
-                        .unwrap_or_else(|| selectors.clone()))
-                    },
-                    Where(ref selectors) => {
-                        Where(
-                            replace_parent_on_selector_list(
-                                selectors.slice(),
-                                parent,
-                                &mut specificity,
-                                &mut flags,
-                                /* propagate_specificity = */ false,
-                                SelectorFlags::for_nesting(),
-                            )
-                            .unwrap_or_else(|| selectors.clone()),
-                        )
-                    },
-                    Has(ref selectors) => Has(replace_parent_on_relative_selector_list(
-                        selectors,
+                        .unwrap_or_else(|| selectors.clone()),
+                    )
+                },
+                Is(ref selectors) => {
+                    Is(replace_parent_on_selector_list(
+                        selectors.slice(),
                         parent,
                         &mut specificity,
                         &mut flags,
+                        /* propagate_specificity = */ true,
                         SelectorFlags::for_nesting(),
                     )
-                    .into_boxed_slice()),
-
-                    Host(Some(ref selector)) => Host(Some(replace_parent_on_selector(
-                        selector,
-                        parent,
-                        &mut specificity,
-                        &mut flags,
-                        SelectorFlags::for_nesting() - SelectorFlags::HAS_NON_FEATURELESS_COMPONENT,
-                    ))),
-                    NthOf(ref data) => {
-                        let selectors = replace_parent_on_selector_list(
-                            data.selectors(),
+                    .unwrap_or_else(|| selectors.clone()))
+                },
+                Where(ref selectors) => {
+                    Where(
+                        replace_parent_on_selector_list(
+                            selectors.slice(),
                             parent,
                             &mut specificity,
                             &mut flags,
-                            /* propagate_specificity = */ true,
+                            /* propagate_specificity = */ false,
                             SelectorFlags::for_nesting(),
-                        );
-                        NthOf(match selectors {
-                            Some(s) => {
-                                NthOfSelectorData::new(data.nth_data(), s.slice().iter().cloned())
-                            },
-                            None => data.clone(),
-                        })
-                    },
-                    Slotted(ref selector) => Slotted(replace_parent_on_selector(
-                        selector,
+                        )
+                        .unwrap_or_else(|| selectors.clone()),
+                    )
+                },
+                Has(ref selectors) => Has(replace_parent_on_relative_selector_list(
+                    selectors,
+                    parent,
+                    &mut specificity,
+                    &mut flags,
+                    SelectorFlags::for_nesting(),
+                )
+                .into_boxed_slice()),
+
+                Host(Some(ref selector)) => Host(Some(replace_parent_on_selector(
+                    selector,
+                    parent,
+                    &mut specificity,
+                    &mut flags,
+                    SelectorFlags::for_nesting() - SelectorFlags::HAS_NON_FEATURELESS_COMPONENT,
+                ))),
+                NthOf(ref data) => {
+                    let selectors = replace_parent_on_selector_list(
+                        data.selectors(),
                         parent,
                         &mut specificity,
                         &mut flags,
+                        /* propagate_specificity = */ true,
                         SelectorFlags::for_nesting(),
-                    )),
-                }
-            });
-            UniqueArc::from_header_and_iter(Default::default(), iter)
-        };
+                    );
+                    NthOf(match selectors {
+                        Some(s) => {
+                            NthOfSelectorData::new(data.nth_data(), s.slice().iter().cloned())
+                        },
+                        None => data.clone(),
+                    })
+                },
+                Slotted(ref selector) => Slotted(replace_parent_on_selector(
+                    selector,
+                    parent,
+                    &mut specificity,
+                    &mut flags,
+                    SelectorFlags::for_nesting(),
+                )),
+            }
+        });
+        let mut items = UniqueArc::from_header_and_iter(Default::default(), iter);
         *items.header_mut() = SpecificityAndFlags {
             specificity: specificity.into(),
             flags,
@@ -2602,9 +2608,14 @@ where
                 // combinator.
                 builder.push_combinator(combinator.unwrap_or(Combinator::Descendant));
             },
-            ParseRelative::ForNesting => {
+            ParseRelative::ForNesting | ParseRelative::ForScope => {
                 if let Ok(combinator) = combinator {
-                    builder.push_simple_selector(Component::ParentSelector);
+                    let selector = match parse_relative {
+                        ParseRelative::ForHas | ParseRelative::No => unreachable!(),
+                        ParseRelative::ForNesting => Component::ParentSelector,
+                        ParseRelative::ForScope => Component::Scope,
+                    };
+                    builder.push_simple_selector(selector);
                     builder.push_combinator(combinator);
                 }
             },
@@ -2643,7 +2654,7 @@ where
 
         builder.push_combinator(combinator);
     }
-    return Ok(Selector(builder.build()));
+    return Ok(Selector(builder.build(parse_relative)));
 }
 
 fn try_parse_combinator<'i, 't, P, Impl>(input: &mut CssParser<'i, 't>) -> Result<Combinator, ()> {
@@ -4375,7 +4386,7 @@ pub mod tests {
             parse("#foo:has(:is(.bar, div .baz).bar)").unwrap()
         );
 
-        let child = parse("#foo").unwrap();
+        let child = parse_relative_expected("#foo", ParseRelative::ForNesting, Some("& #foo")).unwrap();
         assert_eq!(
             child.replace_parent_selector(&parent),
             parse(":is(.bar, div .baz) #foo").unwrap()
diff --git a/servo/components/selectors/tree.rs b/servo/components/selectors/tree.rs
index c1ea8ff5ae..1c440a124d 100644
--- a/servo/components/selectors/tree.rs
+++ b/servo/components/selectors/tree.rs
@@ -134,6 +134,11 @@ pub trait Element: Sized + Clone + Debug {
         case_sensitivity: CaseSensitivity,
     ) -> bool;
 
+    fn has_custom_state(
+        &self,
+        name: &<Self::Impl as SelectorImpl>::Identifier,
+    ) -> bool;
+
     /// Returns the mapping from the `exportparts` attribute in the reverse
     /// direction, that is, in an outer-tree -> inner-tree direction.
     fn imported_part(
diff --git a/servo/components/servo_arc/Cargo.toml b/servo/components/servo_arc/Cargo.toml
index 03b1004bac..51aeb0e1f3 100644
--- a/servo/components/servo_arc/Cargo.toml
+++ b/servo/components/servo_arc/Cargo.toml
@@ -12,7 +12,8 @@ path = "lib.rs"
 
 [features]
 gecko_refcount_logging = []
-servo = ["serde"]
+servo = ["serde", "track_alloc_size"]
+track_alloc_size = []
 
 [dependencies]
 serde = { version = "1.0", optional = true }
diff --git a/servo/components/servo_arc/lib.rs b/servo/components/servo_arc/lib.rs
index 1438ccebfd..c3d27c5bb5 100644
--- a/servo/components/servo_arc/lib.rs
+++ b/servo/components/servo_arc/lib.rs
@@ -35,10 +35,8 @@ use stable_deref_trait::{CloneStableDeref, StableDeref};
 use std::alloc::{self, Layout};
 use std::borrow;
 use std::cmp::Ordering;
-use std::convert::From;
 use std::fmt;
 use std::hash::{Hash, Hasher};
-use std::iter::{ExactSizeIterator, Iterator};
 use std::marker::PhantomData;
 use std::mem::{self, align_of, size_of};
 use std::ops::{Deref, DerefMut};
@@ -122,6 +120,8 @@ impl<T> UniqueArc<T> {
                 .unwrap_or_else(|| alloc::handle_alloc_error(layout))
                 .cast::<ArcInner<mem::MaybeUninit<T>>>();
             ptr::write(&mut p.as_mut().count, atomic::AtomicUsize::new(1));
+            #[cfg(feature = "track_alloc_size")]
+            ptr::write(&mut p.as_mut().alloc_size, layout.size());
 
             #[cfg(feature = "gecko_refcount_logging")]
             {
@@ -171,9 +171,24 @@ unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
 unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
 
 /// The object allocated by an Arc<T>
+///
+/// See https://github.com/mozilla/cbindgen/issues/937 for the derive-{eq,neq}=false. But we don't
+/// use those anyways so we can just disable them.
+/// cbindgen:derive-eq=false
+/// cbindgen:derive-neq=false
 #[repr(C)]
 struct ArcInner<T: ?Sized> {
     count: atomic::AtomicUsize,
+    // NOTE(emilio): This needs to be here so that HeaderSlice<> is deallocated properly if the
+    // allocator relies on getting the right Layout. We don't need to track the right alignment,
+    // since we know that statically.
+    //
+    // This member could be completely avoided once min_specialization feature is stable (by
+    // implementing a trait for HeaderSlice that gives you the right layout). For now, servo-only
+    // since Gecko doesn't need it (its allocator doesn't need the size for the alignments we care
+    // about). See https://github.com/rust-lang/rust/issues/31844.
+    #[cfg(feature = "track_alloc_size")]
+    alloc_size: usize,
     data: T,
 }
 
@@ -192,24 +207,31 @@ impl<T> Arc<T> {
     /// Construct an `Arc<T>`
     #[inline]
     pub fn new(data: T) -> Self {
-        let ptr = Box::into_raw(Box::new(ArcInner {
-            count: atomic::AtomicUsize::new(1),
-            data,
-        }));
+        let layout = Layout::new::<ArcInner<T>>();
+        let p = unsafe {
+            let ptr = ptr::NonNull::new(alloc::alloc(layout))
+                .unwrap_or_else(|| alloc::handle_alloc_error(layout))
+                .cast::<ArcInner<T>>();
+            ptr::write(ptr.as_ptr(), ArcInner {
+                count: atomic::AtomicUsize::new(1),
+                #[cfg(feature = "track_alloc_size")]
+                alloc_size: layout.size(),
+                data,
+            });
+            ptr
+        };
 
         #[cfg(feature = "gecko_refcount_logging")]
         unsafe {
             // FIXME(emilio): Would be so amazing to have
             // std::intrinsics::type_name() around, so that we could also report
             // a real size.
-            NS_LogCtor(ptr as *mut _, b"ServoArc\0".as_ptr() as *const _, 8);
+            NS_LogCtor(p.as_ptr() as *mut _, b"ServoArc\0".as_ptr() as *const _, 8);
         }
 
-        unsafe {
-            Arc {
-                p: ptr::NonNull::new_unchecked(ptr),
-                phantom: PhantomData,
-            }
+        Arc {
+            p,
+            phantom: PhantomData,
         }
     }
 
@@ -266,10 +288,13 @@ impl<T> Arc<T> {
     where
         F: FnOnce(Layout) -> *mut u8,
     {
-        let ptr = alloc(Layout::new::<ArcInner<T>>()) as *mut ArcInner<T>;
+        let layout = Layout::new::<ArcInner<T>>();
+        let ptr = alloc(layout) as *mut ArcInner<T>;
 
         let x = ArcInner {
             count: atomic::AtomicUsize::new(STATIC_REFCOUNT),
+            #[cfg(feature = "track_alloc_size")]
+            alloc_size: layout.size(),
             data,
         };
 
@@ -337,7 +362,14 @@ impl<T: ?Sized> Arc<T> {
     #[inline(never)]
     unsafe fn drop_slow(&mut self) {
         self.record_drop();
-        let _ = Box::from_raw(self.ptr());
+        let inner = self.ptr();
+
+        let layout = Layout::for_value(&*inner);
+        #[cfg(feature = "track_alloc_size")]
+        let layout = Layout::from_size_align_unchecked((*inner).alloc_size, layout.align());
+
+        std::ptr::drop_in_place(inner);
+        alloc::dealloc(inner as *mut _, layout);
     }
 
     /// Test pointer equality between the two Arcs, i.e. they must be the _same_
@@ -711,11 +743,6 @@ impl<H, T> HeaderSlice<H, T> {
     }
 }
 
-#[inline(always)]
-fn divide_rounding_up(dividend: usize, divisor: usize) -> usize {
-    (dividend + divisor - 1) / divisor
-}
-
 impl<H, T> Arc<HeaderSlice<H, T>> {
     /// Creates an Arc for a HeaderSlice using the given header struct and
     /// iterator to generate the slice.
@@ -742,26 +769,17 @@ impl<H, T> Arc<HeaderSlice<H, T>> {
     {
         assert_ne!(size_of::<T>(), 0, "Need to think about ZST");
 
-        let size = size_of::<ArcInner<HeaderSlice<H, T>>>() + size_of::<T>() * num_items;
-        let inner_align = align_of::<ArcInner<HeaderSlice<H, T>>>();
-        debug_assert!(inner_align >= align_of::<T>());
-
-        let ptr: *mut ArcInner<HeaderSlice<H, T>>;
-        unsafe {
+        let layout = Layout::new::<ArcInner<HeaderSlice<H, T>>>();
+        debug_assert!(layout.align() >= align_of::<T>());
+        debug_assert!(layout.align() >= align_of::<usize>());
+        let array_layout = Layout::array::<T>(num_items).expect("Overflow");
+        let (layout, _offset) = layout.extend(array_layout).expect("Overflow");
+        let p = unsafe {
             // Allocate the buffer.
-            let layout = if inner_align <= align_of::<usize>() {
-                Layout::from_size_align_unchecked(size, align_of::<usize>())
-            } else if inner_align <= align_of::<u64>() {
-                // On 32-bit platforms <T> may have 8 byte alignment while usize
-                // has 4 byte aligment.  Use u64 to avoid over-alignment.
-                // This branch will compile away in optimized builds.
-                Layout::from_size_align_unchecked(size, align_of::<u64>())
-            } else {
-                panic!("Over-aligned type not handled");
-            };
-
             let buffer = alloc(layout);
-            ptr = buffer as *mut ArcInner<HeaderSlice<H, T>>;
+            let mut p = ptr::NonNull::new(buffer)
+                .unwrap_or_else(|| alloc::handle_alloc_error(layout))
+                .cast::<ArcInner<HeaderSlice<H, T>>>();
 
             // Write the data.
             //
@@ -772,11 +790,13 @@ impl<H, T> Arc<HeaderSlice<H, T>> {
             } else {
                 atomic::AtomicUsize::new(1)
             };
-            ptr::write(&mut ((*ptr).count), count);
-            ptr::write(&mut ((*ptr).data.header), header);
-            ptr::write(&mut ((*ptr).data.len), num_items);
+            ptr::write(&mut p.as_mut().count, count);
+            #[cfg(feature = "track_alloc_size")]
+            ptr::write(&mut p.as_mut().alloc_size, layout.size());
+            ptr::write(&mut p.as_mut().data.header, header);
+            ptr::write(&mut p.as_mut().data.len, num_items);
             if num_items != 0 {
-                let mut current = std::ptr::addr_of_mut!((*ptr).data.data) as *mut T;
+                let mut current = std::ptr::addr_of_mut!(p.as_mut().data.data) as *mut T;
                 for _ in 0..num_items {
                     ptr::write(
                         current,
@@ -789,20 +809,21 @@ impl<H, T> Arc<HeaderSlice<H, T>> {
                 // We should have consumed the buffer exactly, maybe accounting
                 // for some padding from the alignment.
                 debug_assert!(
-                    (buffer.add(size) as usize - current as *mut u8 as usize) < inner_align
+                    (buffer.add(layout.size()) as usize - current as *mut u8 as usize) < layout.align()
                 );
             }
             assert!(
                 items.next().is_none(),
                 "ExactSizeIterator under-reported length"
             );
-        }
+            p
+        };
         #[cfg(feature = "gecko_refcount_logging")]
         unsafe {
             if !is_static {
                 // FIXME(emilio): Would be so amazing to have
                 // std::intrinsics::type_name() around.
-                NS_LogCtor(ptr as *mut _, b"ServoArc\0".as_ptr() as *const _, 8)
+                NS_LogCtor(p.as_ptr() as *mut _, b"ServoArc\0".as_ptr() as *const _, 8)
             }
         }
 
@@ -812,11 +833,10 @@ impl<H, T> Arc<HeaderSlice<H, T>> {
             size_of::<usize>(),
             "The Arc should be thin"
         );
-        unsafe {
-            Arc {
-                p: ptr::NonNull::new_unchecked(ptr),
-                phantom: PhantomData,
-            }
+
+        Arc {
+            p,
+            phantom: PhantomData,
         }
     }
 
@@ -828,18 +848,7 @@ impl<H, T> Arc<HeaderSlice<H, T>> {
         I: Iterator<Item = T>,
     {
         Arc::from_header_and_iter_alloc(
-            |layout| {
-                // align will only ever be align_of::<usize>() or align_of::<u64>()
-                let align = layout.align();
-                unsafe {
-                    if align == mem::align_of::<usize>() {
-                        Self::allocate_buffer::<usize>(layout.size())
-                    } else {
-                        assert_eq!(align, mem::align_of::<u64>());
-                        Self::allocate_buffer::<u64>(layout.size())
-                    }
-                }
-            },
+            |layout| unsafe { alloc::alloc(layout) },
             header,
             items,
             num_items,
@@ -857,17 +866,6 @@ impl<H, T> Arc<HeaderSlice<H, T>> {
         let len = items.len();
         Self::from_header_and_iter_with_size(header, items, len)
     }
-
-    #[inline]
-    unsafe fn allocate_buffer<W>(size: usize) -> *mut u8 {
-        // We use Vec because the underlying allocation machinery isn't
-        // available in stable Rust. To avoid alignment issues, we allocate
-        // words rather than bytes, rounding up to the nearest word size.
-        let words_to_allocate = divide_rounding_up(size, mem::size_of::<W>());
-        let mut vec = Vec::<W>::with_capacity(words_to_allocate);
-        vec.set_len(words_to_allocate);
-        Box::into_raw(vec.into_boxed_slice()) as *mut W as *mut u8
-    }
 }
 
 /// This is functionally equivalent to Arc<(H, [T])>
diff --git a/servo/components/style/Cargo.toml b/servo/components/style/Cargo.toml
index acf1bcf6fe..d6e37d4903 100644
--- a/servo/components/style/Cargo.toml
+++ b/servo/components/style/Cargo.toml
@@ -21,8 +21,6 @@ gecko = ["nsstring", "serde", "style_traits/gecko", "bindgen", "regex", "toml",
 servo = ["serde", "style_traits/servo", "servo_atoms", "servo_config", "html5ever",
          "cssparser/serde", "encoding_rs", "malloc_size_of/servo", "arrayvec/use_union",
          "servo_url", "string_cache", "to_shmem/servo", "servo_arc/servo"]
-servo-layout-2013 = []
-servo-layout-2020 = []
 gecko_debug = []
 gecko_refcount_logging = []
 
diff --git a/servo/components/style/animation.rs b/servo/components/style/animation.rs
index b865120aba..1cab5da84e 100644
--- a/servo/components/style/animation.rs
+++ b/servo/components/style/animation.rs
@@ -1273,9 +1273,10 @@ pub fn start_transitions_if_applicable(
 ) -> PropertyDeclarationIdSet {
     let mut properties_that_transition = PropertyDeclarationIdSet::default();
     for transition in new_style.transition_properties() {
-        let physical_property = PropertyDeclarationId::Longhand(
-            transition.longhand_id.to_physical(new_style.writing_mode),
-        );
+        let physical_property = transition
+            .property
+            .as_borrowed()
+            .to_physical(new_style.writing_mode);
         if properties_that_transition.contains(physical_property) {
             continue;
         }
diff --git a/servo/components/style/applicable_declarations.rs b/servo/components/style/applicable_declarations.rs
index 96049b76e3..b2fb05b0b8 100644
--- a/servo/components/style/applicable_declarations.rs
+++ b/servo/components/style/applicable_declarations.rs
@@ -142,8 +142,9 @@ pub struct ApplicableDeclarationBlock {
     /// The style source, either a style rule, or a property declaration block.
     #[ignore_malloc_size_of = "Arc"]
     pub source: StyleSource,
-    /// The bits containing the source order, cascade level, and shadow cascade
-    /// order.
+    /// Order of appearance in which this rule appears - Set to 0 if not relevant
+    /// (e.g. Declaration from `style="/*...*/"`, presentation hints, animations
+    /// - See `CascadePriority` instead).
     source_order: u32,
     /// The specificity of the selector.
     pub specificity: u32,
diff --git a/servo/components/style/bloom.rs b/servo/components/style/bloom.rs
index 824acb7114..63be881505 100644
--- a/servo/components/style/bloom.rs
+++ b/servo/components/style/bloom.rs
@@ -8,6 +8,7 @@
 #![deny(missing_docs)]
 
 use crate::dom::{SendElement, TElement};
+use crate::LocalName;
 use atomic_refcell::{AtomicRefCell, AtomicRefMut};
 use owning_ref::OwningHandle;
 use selectors::bloom::BloomFilter;
@@ -107,8 +108,8 @@ impl<E: TElement> PushedElement<E> {
 /// We do this for attributes that are very common but not commonly used in
 /// selectors.
 #[inline]
-pub fn is_attr_name_excluded_from_filter(atom: &crate::Atom) -> bool {
-    *atom == atom!("class") || *atom == atom!("id") || *atom == atom!("style")
+pub fn is_attr_name_excluded_from_filter(name: &LocalName) -> bool {
+    *name == local_name!("class") || *name == local_name!("id") || *name == local_name!("style")
 }
 
 /// Gather all relevant hash for fast-reject filters from an element.
diff --git a/servo/components/style/build.rs b/servo/components/style/build.rs
index 2247e87618..4b27edbe2c 100644
--- a/servo/components/style/build.rs
+++ b/servo/components/style/build.rs
@@ -71,16 +71,12 @@ fn generate_properties(engine: &str) {
 fn main() {
     let gecko = cfg!(feature = "gecko");
     let servo = cfg!(feature = "servo");
-    let l2013 = cfg!(feature = "servo-layout-2013");
-    let l2020 = cfg!(feature = "servo-layout-2020");
-    let engine = match (gecko, servo, l2013, l2020) {
-        (true, false, false, false) => "gecko",
-        (false, true, true, false) => "servo-2013",
-        (false, true, false, true) => "servo-2020",
+    let engine = match (gecko, servo) {
+        (true, false) => "gecko",
+        (false, true) => "servo",
         _ => panic!(
             "\n\n\
-             The style crate requires enabling one of its 'servo' or 'gecko' feature flags \
-             and, in the 'servo' case, one of 'servo-layout-2013' or 'servo-layout-2020'.\
+             The style crate requires enabling one of its 'servo' or 'gecko' feature flags. \
              \n\n"
         ),
     };
diff --git a/servo/components/style/color/color_function.rs b/servo/components/style/color/color_function.rs
new file mode 100644
index 0000000000..2edb4fff3b
--- /dev/null
+++ b/servo/components/style/color/color_function.rs
@@ -0,0 +1,198 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Output of parsing a color function, e.g. rgb(..), hsl(..), color(..)
+
+use crate::values::normalize;
+use cssparser::color::{PredefinedColorSpace, OPAQUE};
+
+use super::{
+    component::ColorComponent,
+    convert::normalize_hue,
+    parsing::{NumberOrAngle, NumberOrPercentage},
+    AbsoluteColor, ColorSpace,
+};
+
+/// Represents a specified color function.
+#[derive(Debug)]
+pub enum ColorFunction {
+    /// <https://drafts.csswg.org/css-color-4/#rgb-functions>
+    Rgb(
+        ColorComponent<u8>,                 // red
+        ColorComponent<u8>,                 // green
+        ColorComponent<u8>,                 // blue
+        ColorComponent<NumberOrPercentage>, // alpha
+    ),
+    /// <https://drafts.csswg.org/css-color-4/#the-hsl-notation>
+    Hsl(
+        ColorComponent<NumberOrAngle>,      // hue
+        ColorComponent<NumberOrPercentage>, // saturation
+        ColorComponent<NumberOrPercentage>, // lightness
+        ColorComponent<NumberOrPercentage>, // alpha
+    ),
+    /// <https://drafts.csswg.org/css-color-4/#the-hwb-notation>
+    Hwb(
+        ColorComponent<NumberOrAngle>,      // hue
+        ColorComponent<NumberOrPercentage>, // whiteness
+        ColorComponent<NumberOrPercentage>, // blackness
+        ColorComponent<NumberOrPercentage>, // alpha
+    ),
+    /// <https://drafts.csswg.org/css-color-4/#specifying-lab-lch>
+    Lab(
+        ColorComponent<NumberOrPercentage>, // lightness
+        ColorComponent<NumberOrPercentage>, // a
+        ColorComponent<NumberOrPercentage>, // b
+        ColorComponent<NumberOrPercentage>, // alpha
+    ),
+    /// <https://drafts.csswg.org/css-color-4/#specifying-lab-lch>
+    Lch(
+        ColorComponent<NumberOrPercentage>, // lightness
+        ColorComponent<NumberOrPercentage>, // chroma
+        ColorComponent<NumberOrAngle>,      // hue
+        ColorComponent<NumberOrPercentage>, // alpha
+    ),
+    /// <https://drafts.csswg.org/css-color-4/#specifying-oklab-oklch>
+    Oklab(
+        ColorComponent<NumberOrPercentage>, // lightness
+        ColorComponent<NumberOrPercentage>, // a
+        ColorComponent<NumberOrPercentage>, // b
+        ColorComponent<NumberOrPercentage>, // alpha
+    ),
+    /// <https://drafts.csswg.org/css-color-4/#specifying-oklab-oklch>
+    Oklch(
+        ColorComponent<NumberOrPercentage>, // lightness
+        ColorComponent<NumberOrPercentage>, // chroma
+        ColorComponent<NumberOrAngle>,      // hue
+        ColorComponent<NumberOrPercentage>, // alpha
+    ),
+    /// <https://drafts.csswg.org/css-color-4/#color-function>
+    Color(
+        PredefinedColorSpace,
+        ColorComponent<NumberOrPercentage>, // red / x
+        ColorComponent<NumberOrPercentage>, // green / y
+        ColorComponent<NumberOrPercentage>, // blue / z
+        ColorComponent<NumberOrPercentage>, // alpha
+    ),
+}
+
+impl ColorFunction {
+    /// Try to resolve the color function to an [`AbsoluteColor`] that does not
+    /// contain any variables (currentcolor, color components, etc.).
+    pub fn resolve_to_absolute(&self) -> AbsoluteColor {
+        macro_rules! value {
+            ($v:expr) => {{
+                match $v {
+                    ColorComponent::None => None,
+                    // value should be Copy.
+                    ColorComponent::Value(value) => Some(*value),
+                }
+            }};
+        }
+
+        macro_rules! alpha {
+            ($alpha:expr) => {{
+                value!($alpha).map(|value| normalize(value.to_number(1.0)).clamp(0.0, OPAQUE))
+            }};
+        }
+
+        match self {
+            ColorFunction::Rgb(r, g, b, alpha) => {
+                let r = value!(r).unwrap_or(0);
+                let g = value!(g).unwrap_or(0);
+                let b = value!(b).unwrap_or(0);
+
+                AbsoluteColor::srgb_legacy(r, g, b, alpha!(alpha).unwrap_or(0.0))
+            },
+            ColorFunction::Hsl(h, s, l, alpha) => {
+                // Percent reference range for S and L: 0% = 0.0, 100% = 100.0
+                const LIGHTNESS_RANGE: f32 = 100.0;
+                const SATURATION_RANGE: f32 = 100.0;
+
+                AbsoluteColor::new(
+                    ColorSpace::Hsl,
+                    value!(h).map(|angle| normalize_hue(angle.degrees())),
+                    value!(s).map(|s| s.to_number(SATURATION_RANGE).clamp(0.0, SATURATION_RANGE)),
+                    value!(l).map(|l| l.to_number(LIGHTNESS_RANGE).clamp(0.0, LIGHTNESS_RANGE)),
+                    alpha!(alpha),
+                )
+            },
+            ColorFunction::Hwb(h, w, b, alpha) => {
+                // Percent reference range for W and B: 0% = 0.0, 100% = 100.0
+                const WHITENESS_RANGE: f32 = 100.0;
+                const BLACKNESS_RANGE: f32 = 100.0;
+
+                AbsoluteColor::new(
+                    ColorSpace::Hwb,
+                    value!(h).map(|angle| normalize_hue(angle.degrees())),
+                    value!(w).map(|w| w.to_number(WHITENESS_RANGE).clamp(0.0, WHITENESS_RANGE)),
+                    value!(b).map(|b| b.to_number(BLACKNESS_RANGE).clamp(0.0, BLACKNESS_RANGE)),
+                    alpha!(alpha),
+                )
+            },
+            ColorFunction::Lab(l, a, b, alpha) => {
+                // for L: 0% = 0.0, 100% = 100.0
+                // for a and b: -100% = -125, 100% = 125
+                const LIGHTNESS_RANGE: f32 = 100.0;
+                const A_B_RANGE: f32 = 125.0;
+
+                AbsoluteColor::new(
+                    ColorSpace::Lab,
+                    value!(l).map(|l| l.to_number(LIGHTNESS_RANGE)),
+                    value!(a).map(|a| a.to_number(A_B_RANGE)),
+                    value!(b).map(|b| b.to_number(A_B_RANGE)),
+                    alpha!(alpha),
+                )
+            },
+            ColorFunction::Lch(l, c, h, alpha) => {
+                // for L: 0% = 0.0, 100% = 100.0
+                // for C: 0% = 0, 100% = 150
+                const LIGHTNESS_RANGE: f32 = 100.0;
+                const CHROMA_RANGE: f32 = 150.0;
+
+                AbsoluteColor::new(
+                    ColorSpace::Lch,
+                    value!(l).map(|l| l.to_number(LIGHTNESS_RANGE)),
+                    value!(c).map(|c| c.to_number(CHROMA_RANGE)),
+                    value!(h).map(|angle| normalize_hue(angle.degrees())),
+                    alpha!(alpha),
+                )
+            },
+            ColorFunction::Oklab(l, a, b, alpha) => {
+                // for L: 0% = 0.0, 100% = 1.0
+                // for a and b: -100% = -0.4, 100% = 0.4
+                const LIGHTNESS_RANGE: f32 = 1.0;
+                const A_B_RANGE: f32 = 0.4;
+
+                AbsoluteColor::new(
+                    ColorSpace::Oklab,
+                    value!(l).map(|l| l.to_number(LIGHTNESS_RANGE)),
+                    value!(a).map(|a| a.to_number(A_B_RANGE)),
+                    value!(b).map(|b| b.to_number(A_B_RANGE)),
+                    alpha!(alpha),
+                )
+            },
+            ColorFunction::Oklch(l, c, h, alpha) => {
+                // for L: 0% = 0.0, 100% = 1.0
+                // for C: 0% = 0.0 100% = 0.4
+                const LIGHTNESS_RANGE: f32 = 1.0;
+                const CHROMA_RANGE: f32 = 0.4;
+
+                AbsoluteColor::new(
+                    ColorSpace::Oklch,
+                    value!(l).map(|l| l.to_number(LIGHTNESS_RANGE)),
+                    value!(c).map(|c| c.to_number(CHROMA_RANGE)),
+                    value!(h).map(|angle| normalize_hue(angle.degrees())),
+                    alpha!(alpha),
+                )
+            },
+            ColorFunction::Color(color_space, r, g, b, alpha) => AbsoluteColor::new(
+                (*color_space).into(),
+                value!(r).map(|c| c.to_number(1.0)),
+                value!(g).map(|c| c.to_number(1.0)),
+                value!(b).map(|c| c.to_number(1.0)),
+                alpha!(alpha),
+            ),
+        }
+    }
+}
diff --git a/servo/components/style/color/component.rs b/servo/components/style/color/component.rs
index 9f101a460c..5f9d8a137e 100644
--- a/servo/components/style/color/component.rs
+++ b/servo/components/style/color/component.rs
@@ -4,8 +4,18 @@
 
 //! Parse/serialize and resolve a single color component.
 
+use crate::{
+    parser::ParserContext,
+    values::{
+        generics::calc::CalcUnits,
+        specified::calc::{CalcNode as SpecifiedCalcNode, Leaf as SpecifiedLeaf},
+    },
+};
+use cssparser::{Parser, Token};
+use style_traits::{ParseError, StyleParseErrorKind};
+
 /// A single color component.
-#[derive(Clone, MallocSizeOf, PartialEq, ToShmem)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToShmem)]
 pub enum ColorComponent<ValueType> {
     /// The "none" keyword.
     None,
@@ -46,3 +56,49 @@ impl<ValueType> ColorComponent<ValueType> {
         }
     }
 }
+
+/// An utility trait that allows the construction of [ColorComponent]
+/// `ValueType`'s after parsing a color component.
+pub trait ColorComponentType: Sized {
+    /// Return the [CalcUnits] flags that the impl can handle.
+    fn units() -> CalcUnits;
+
+    /// Try to create a new component from the given token.
+    fn try_from_token(token: &Token) -> Result<Self, ()>;
+
+    /// Try to create a new component from the given [CalcNodeLeaf] that was
+    /// resolved from a [CalcNode].
+    fn try_from_leaf(leaf: &SpecifiedLeaf) -> Result<Self, ()>;
+}
+
+impl<ValueType: ColorComponentType> ColorComponent<ValueType> {
+    /// Parse a single [ColorComponent].
+    pub fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        allow_none: bool,
+    ) -> Result<Self, ParseError<'i>> {
+        let location = input.current_source_location();
+
+        match *input.next()? {
+            Token::Ident(ref value) if allow_none && value.eq_ignore_ascii_case("none") => {
+                Ok(ColorComponent::None)
+            },
+            Token::Function(ref name) => {
+                let function = SpecifiedCalcNode::math_function(context, name, location)?;
+                let node = SpecifiedCalcNode::parse(context, input, function, ValueType::units())?;
+
+                let Ok(resolved_leaf) = node.resolve() else {
+                    return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+                };
+
+                ValueType::try_from_leaf(&resolved_leaf)
+                    .map(Self::Value)
+                    .map_err(|_| location.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+            },
+            ref t => ValueType::try_from_token(t)
+                .map(Self::Value)
+                .map_err(|_| location.new_unexpected_token_error(t.clone())),
+        }
+    }
+}
diff --git a/servo/components/style/color/mix.rs b/servo/components/style/color/mix.rs
index bcc4628575..3b3970e1e0 100644
--- a/servo/components/style/color/mix.rs
+++ b/servo/components/style/color/mix.rs
@@ -402,7 +402,8 @@ fn adjust_hue(left: &mut f32, right: &mut f32, hue_interpolation: HueInterpolati
         // https://drafts.csswg.org/css-color/#longer
         HueInterpolationMethod::Longer => {
             let delta = *right - *left;
-            if 0. < delta && delta < 180. {
+            // In the specific case of delta == 0 we need to use Decreasing
+            if 0. <= delta && delta < 180. {
                 *left += 360.;
             } else if -180. < delta && delta <= 0. {
                 *right += 360.;
diff --git a/servo/components/style/color/mod.rs b/servo/components/style/color/mod.rs
index 6f35daaa8a..f7e661cddf 100644
--- a/servo/components/style/color/mod.rs
+++ b/servo/components/style/color/mod.rs
@@ -4,9 +4,13 @@
 
 //! Color support functions.
 
-pub mod component;
+/// cbindgen:ignore
+mod color_function;
+
 /// cbindgen:ignore
 pub mod convert;
+
+pub mod component;
 pub mod mix;
 pub mod parsing;
 mod to_css;
diff --git a/servo/components/style/color/parsing.rs b/servo/components/style/color/parsing.rs
index 1ae32c4ad7..68bcee6c56 100644
--- a/servo/components/style/color/parsing.rs
+++ b/servo/components/style/color/parsing.rs
@@ -8,14 +8,34 @@
 //! Relative colors, color-mix, system colors, and other such things require better calc() support
 //! and integration.
 
-use crate::color::component::ColorComponent;
-use cssparser::color::{
-    clamp_floor_256_f32, clamp_unit_f32, parse_hash_color, PredefinedColorSpace, OPAQUE,
+use super::{
+    color_function::ColorFunction,
+    component::{ColorComponent, ColorComponentType},
+    AbsoluteColor,
+};
+use crate::{
+    parser::ParserContext,
+    values::{
+        generics::calc::CalcUnits,
+        specified::{
+            angle::Angle as SpecifiedAngle, calc::Leaf as SpecifiedLeaf,
+            color::Color as SpecifiedColor,
+        },
+    },
+};
+use cssparser::{
+    color::{clamp_floor_256_f32, clamp_unit_f32, parse_hash_color, PredefinedColorSpace, OPAQUE},
+    match_ignore_ascii_case, CowRcStr, Parser, Token,
 };
-use cssparser::{match_ignore_ascii_case, CowRcStr, Parser, Token};
 use std::str::FromStr;
 use style_traits::{ParseError, StyleParseErrorKind};
 
+/// Returns true if the relative color syntax pref is enabled.
+#[inline]
+pub fn rcs_enabled() -> bool {
+    static_prefs::pref!("layout.css.relative-color-syntax.enabled")
+}
+
 impl From<u8> for ColorComponent<u8> {
     #[inline]
     fn from(value: u8) -> Self {
@@ -29,56 +49,39 @@ impl From<u8> for ColorComponent<u8> {
 /// CSS escaping (if relevant) should be resolved before calling this function.
 /// (For example, the value of an `Ident` token is fine.)
 #[inline]
-pub fn parse_color_keyword<Output>(ident: &str) -> Result<Output, ()>
-where
-    Output: FromParsedColor,
-{
+pub fn parse_color_keyword(ident: &str) -> Result<SpecifiedColor, ()> {
     Ok(match_ignore_ascii_case! { ident,
-        "transparent" => Output::from_rgba(
-            0u8.into(),
-            0u8.into(),
-            0u8.into(),
-            ColorComponent::Value(NumberOrPercentage::Number { value: 0.0 }),
-        ),
-        "currentcolor" => Output::from_current_color(),
+        "transparent" => {
+            SpecifiedColor::from_absolute_color(AbsoluteColor::srgb_legacy(0u8, 0u8, 0u8, 0.0))
+        },
+        "currentcolor" => SpecifiedColor::CurrentColor,
         _ => {
             let (r, g, b) = cssparser::color::parse_named_color(ident)?;
-            Output::from_rgba(
-                r.into(),
-                g.into(),
-                b.into(),
-                ColorComponent::Value(NumberOrPercentage::Number { value: OPAQUE }),
-            )
+            SpecifiedColor::from_absolute_color(AbsoluteColor::srgb_legacy(r, g, b, OPAQUE))
         },
     })
 }
 
 /// Parse a CSS color using the specified [`ColorParser`] and return a new color
 /// value on success.
-pub fn parse_color_with<'i, 't, P>(
-    color_parser: &P,
+pub fn parse_color_with<'i, 't>(
+    color_parser: &ColorParser<'_, '_>,
     input: &mut Parser<'i, 't>,
-) -> Result<P::Output, ParseError<'i>>
-where
-    P: ColorParser<'i>,
-{
+) -> Result<SpecifiedColor, ParseError<'i>> {
     let location = input.current_source_location();
     let token = input.next()?;
     match *token {
         Token::Hash(ref value) | Token::IDHash(ref value) => parse_hash_color(value.as_bytes())
             .map(|(r, g, b, a)| {
-                P::Output::from_rgba(
-                    r.into(),
-                    g.into(),
-                    b.into(),
-                    ColorComponent::Value(NumberOrPercentage::Number { value: a }),
-                )
+                SpecifiedColor::from_absolute_color(AbsoluteColor::srgb_legacy(r, g, b, a))
             }),
         Token::Ident(ref value) => parse_color_keyword(value),
         Token::Function(ref name) => {
             let name = name.clone();
             return input.parse_nested_block(|arguments| {
-                parse_color_function(color_parser, name, arguments)
+                Ok(SpecifiedColor::from_absolute_color(
+                    parse_color_function(color_parser, name, arguments)?.resolve_to_absolute(),
+                ))
             });
         },
         _ => Err(()),
@@ -88,22 +91,19 @@ where
 
 /// Parse one of the color functions: rgba(), lab(), color(), etc.
 #[inline]
-fn parse_color_function<'i, 't, P>(
-    color_parser: &P,
+fn parse_color_function<'i, 't>(
+    color_parser: &ColorParser<'_, '_>,
     name: CowRcStr<'i>,
     arguments: &mut Parser<'i, 't>,
-) -> Result<P::Output, ParseError<'i>>
-where
-    P: ColorParser<'i>,
-{
+) -> Result<ColorFunction, ParseError<'i>> {
     let color = match_ignore_ascii_case! { &name,
         "rgb" | "rgba" => parse_rgb(color_parser, arguments),
         "hsl" | "hsla" => parse_hsl(color_parser, arguments),
         "hwb" => parse_hwb(color_parser, arguments),
-        "lab" => parse_lab_like(color_parser, arguments, P::Output::from_lab),
-        "lch" => parse_lch_like(color_parser, arguments, P::Output::from_lch),
-        "oklab" => parse_lab_like(color_parser, arguments, P::Output::from_oklab),
-        "oklch" => parse_lch_like(color_parser, arguments, P::Output::from_oklch),
+        "lab" => parse_lab_like(color_parser, arguments, ColorFunction::Lab),
+        "lch" => parse_lch_like(color_parser, arguments, ColorFunction::Lch),
+        "oklab" => parse_lab_like(color_parser, arguments, ColorFunction::Oklab),
+        "oklch" => parse_lch_like(color_parser, arguments, ColorFunction::Oklch),
         "color" => parse_color_with_color_space(color_parser, arguments),
         _ => return Err(arguments.new_unexpected_token_error(Token::Ident(name))),
     }?;
@@ -113,13 +113,10 @@ where
     Ok(color)
 }
 
-fn parse_legacy_alpha<'i, 't, P>(
-    color_parser: &P,
+fn parse_legacy_alpha<'i, 't>(
+    color_parser: &ColorParser<'_, '_>,
     arguments: &mut Parser<'i, 't>,
-) -> Result<ColorComponent<NumberOrPercentage>, ParseError<'i>>
-where
-    P: ColorParser<'i>,
-{
+) -> Result<ColorComponent<NumberOrPercentage>, ParseError<'i>> {
     if !arguments.is_exhausted() {
         arguments.expect_comma()?;
         color_parser.parse_number_or_percentage(arguments, false)
@@ -130,13 +127,10 @@ where
     }
 }
 
-fn parse_modern_alpha<'i, 't, P>(
-    color_parser: &P,
+fn parse_modern_alpha<'i, 't>(
+    color_parser: &ColorParser<'_, '_>,
     arguments: &mut Parser<'i, 't>,
-) -> Result<ColorComponent<NumberOrPercentage>, ParseError<'i>>
-where
-    P: ColorParser<'i>,
-{
+) -> Result<ColorComponent<NumberOrPercentage>, ParseError<'i>> {
     if !arguments.is_exhausted() {
         arguments.expect_delim('/')?;
         color_parser.parse_number_or_percentage(arguments, true)
@@ -157,22 +151,45 @@ impl ColorComponent<NumberOrPercentage> {
     }
 }
 
+/// Parse the relative color syntax "from" syntax `from <color>`.
+fn parse_origin_color<'i, 't>(
+    color_parser: &ColorParser<'_, '_>,
+    arguments: &mut Parser<'i, 't>,
+) -> Result<Option<SpecifiedColor>, ParseError<'i>> {
+    if !rcs_enabled() {
+        return Ok(None);
+    }
+
+    // Not finding the from keyword is not an error, it just means we don't
+    // have an origin color.
+    if arguments
+        .try_parse(|p| p.expect_ident_matching("from"))
+        .is_err()
+    {
+        return Ok(None);
+    }
+
+    // We still fail if we can't parse the origin color.
+    parse_color_with(color_parser, arguments).map(|color| Some(color))
+}
+
 #[inline]
-fn parse_rgb<'i, 't, P>(
-    color_parser: &P,
+fn parse_rgb<'i, 't>(
+    color_parser: &ColorParser<'_, '_>,
     arguments: &mut Parser<'i, 't>,
-) -> Result<P::Output, ParseError<'i>>
-where
-    P: ColorParser<'i>,
-{
+) -> Result<ColorFunction, ParseError<'i>> {
+    let origin_color = parse_origin_color(color_parser, arguments)?;
+
     let location = arguments.current_source_location();
 
     let maybe_red = color_parser.parse_number_or_percentage(arguments, true)?;
 
     // If the first component is not "none" and is followed by a comma, then we
-    // are parsing the legacy syntax.
-    let is_legacy_syntax =
-        !maybe_red.is_none() && arguments.try_parse(|p| p.expect_comma()).is_ok();
+    // are parsing the legacy syntax.  Legacy syntax also doesn't support an
+    // origin color.
+    let is_legacy_syntax = origin_color.is_none() &&
+        !maybe_red.is_none() &&
+        arguments.try_parse(|p| p.expect_comma()).is_ok();
 
     let (red, green, blue, alpha) = if is_legacy_syntax {
         let Ok(is_percentage) = maybe_red.is_percentage() else {
@@ -217,25 +234,26 @@ where
         (red, green, blue, alpha)
     };
 
-    Ok(P::Output::from_rgba(red, green, blue, alpha))
+    Ok(ColorFunction::Rgb(red, green, blue, alpha))
 }
 
 /// Parses hsl syntax.
 ///
 /// <https://drafts.csswg.org/css-color/#the-hsl-notation>
 #[inline]
-fn parse_hsl<'i, 't, P>(
-    color_parser: &P,
+fn parse_hsl<'i, 't>(
+    color_parser: &ColorParser<'_, '_>,
     arguments: &mut Parser<'i, 't>,
-) -> Result<P::Output, ParseError<'i>>
-where
-    P: ColorParser<'i>,
-{
+) -> Result<ColorFunction, ParseError<'i>> {
+    let origin_color = parse_origin_color(color_parser, arguments)?;
+
     let hue = color_parser.parse_number_or_angle(arguments, true)?;
 
     // If the hue is not "none" and is followed by a comma, then we are parsing
-    // the legacy syntax.
-    let is_legacy_syntax = !hue.is_none() && arguments.try_parse(|p| p.expect_comma()).is_ok();
+    // the legacy syntax. Legacy syntax also doesn't support an origin color.
+    let is_legacy_syntax = origin_color.is_none() &&
+        !hue.is_none() &&
+        arguments.try_parse(|p| p.expect_comma()).is_ok();
 
     let (saturation, lightness, alpha) = if is_legacy_syntax {
         let saturation = color_parser
@@ -260,29 +278,28 @@ where
         )
     };
 
-    Ok(P::Output::from_hsl(hue, saturation, lightness, alpha))
+    Ok(ColorFunction::Hsl(hue, saturation, lightness, alpha))
 }
 
 /// Parses hwb syntax.
 ///
 /// <https://drafts.csswg.org/css-color/#the-hbw-notation>
 #[inline]
-fn parse_hwb<'i, 't, P>(
-    color_parser: &P,
+fn parse_hwb<'i, 't>(
+    color_parser: &ColorParser<'_, '_>,
     arguments: &mut Parser<'i, 't>,
-) -> Result<P::Output, ParseError<'i>>
-where
-    P: ColorParser<'i>,
-{
+) -> Result<ColorFunction, ParseError<'i>> {
+    let _origin_color = parse_origin_color(color_parser, arguments)?;
+
     let (hue, whiteness, blackness, alpha) = parse_components(
         color_parser,
         arguments,
-        P::parse_number_or_angle,
-        P::parse_number_or_percentage,
-        P::parse_number_or_percentage,
+        ColorParser::parse_number_or_angle,
+        ColorParser::parse_number_or_percentage,
+        ColorParser::parse_number_or_percentage,
     )?;
 
-    Ok(P::Output::from_hwb(hue, whiteness, blackness, alpha))
+    Ok(ColorFunction::Hwb(hue, whiteness, blackness, alpha))
 }
 
 type IntoLabFn<Output> = fn(
@@ -293,20 +310,19 @@ type IntoLabFn<Output> = fn(
 ) -> Output;
 
 #[inline]
-fn parse_lab_like<'i, 't, P>(
-    color_parser: &P,
+fn parse_lab_like<'i, 't>(
+    color_parser: &ColorParser<'_, '_>,
     arguments: &mut Parser<'i, 't>,
-    into_color: IntoLabFn<P::Output>,
-) -> Result<P::Output, ParseError<'i>>
-where
-    P: ColorParser<'i>,
-{
+    into_color: IntoLabFn<ColorFunction>,
+) -> Result<ColorFunction, ParseError<'i>> {
+    let _origin_color = parse_origin_color(color_parser, arguments)?;
+
     let (lightness, a, b, alpha) = parse_components(
         color_parser,
         arguments,
-        P::parse_number_or_percentage,
-        P::parse_number_or_percentage,
-        P::parse_number_or_percentage,
+        ColorParser::parse_number_or_percentage,
+        ColorParser::parse_number_or_percentage,
+        ColorParser::parse_number_or_percentage,
     )?;
 
     Ok(into_color(lightness, a, b, alpha))
@@ -320,20 +336,19 @@ type IntoLchFn<Output> = fn(
 ) -> Output;
 
 #[inline]
-fn parse_lch_like<'i, 't, P>(
-    color_parser: &P,
+fn parse_lch_like<'i, 't>(
+    color_parser: &ColorParser<'_, '_>,
     arguments: &mut Parser<'i, 't>,
-    into_color: IntoLchFn<P::Output>,
-) -> Result<P::Output, ParseError<'i>>
-where
-    P: ColorParser<'i>,
-{
+    into_color: IntoLchFn<ColorFunction>,
+) -> Result<ColorFunction, ParseError<'i>> {
+    let _origin_color = parse_origin_color(color_parser, arguments)?;
+
     let (lightness, chroma, hue, alpha) = parse_components(
         color_parser,
         arguments,
-        P::parse_number_or_percentage,
-        P::parse_number_or_percentage,
-        P::parse_number_or_angle,
+        ColorParser::parse_number_or_percentage,
+        ColorParser::parse_number_or_percentage,
+        ColorParser::parse_number_or_angle,
     )?;
 
     Ok(into_color(lightness, chroma, hue, alpha))
@@ -341,13 +356,12 @@ where
 
 /// Parse the color() function.
 #[inline]
-fn parse_color_with_color_space<'i, 't, P>(
-    color_parser: &P,
+fn parse_color_with_color_space<'i, 't>(
+    color_parser: &ColorParser<'_, '_>,
     arguments: &mut Parser<'i, 't>,
-) -> Result<P::Output, ParseError<'i>>
-where
-    P: ColorParser<'i>,
-{
+) -> Result<ColorFunction, ParseError<'i>> {
+    let _origin_color = parse_origin_color(color_parser, arguments)?;
+
     let color_space = {
         let location = arguments.current_source_location();
 
@@ -359,18 +373,12 @@ where
     let (c1, c2, c3, alpha) = parse_components(
         color_parser,
         arguments,
-        P::parse_number_or_percentage,
-        P::parse_number_or_percentage,
-        P::parse_number_or_percentage,
+        ColorParser::parse_number_or_percentage,
+        ColorParser::parse_number_or_percentage,
+        ColorParser::parse_number_or_percentage,
     )?;
 
-    Ok(P::Output::from_color_function(
-        color_space,
-        c1,
-        c2,
-        c3,
-        alpha,
-    ))
+    Ok(ColorFunction::Color(color_space, c1, c2, c3, alpha))
 }
 
 type ComponentParseResult<'i, R1, R2, R3> = Result<
@@ -384,18 +392,29 @@ type ComponentParseResult<'i, R1, R2, R3> = Result<
 >;
 
 /// Parse the color components and alpha with the modern [color-4] syntax.
-pub fn parse_components<'i, 't, P, F1, F2, F3, R1, R2, R3>(
-    color_parser: &P,
+pub fn parse_components<'a, 'b: 'a, 'i, 't, F1, F2, F3, R1, R2, R3>(
+    color_parser: &ColorParser<'a, 'b>,
     input: &mut Parser<'i, 't>,
     f1: F1,
     f2: F2,
     f3: F3,
 ) -> ComponentParseResult<'i, R1, R2, R3>
 where
-    P: ColorParser<'i>,
-    F1: FnOnce(&P, &mut Parser<'i, 't>, bool) -> Result<ColorComponent<R1>, ParseError<'i>>,
-    F2: FnOnce(&P, &mut Parser<'i, 't>, bool) -> Result<ColorComponent<R2>, ParseError<'i>>,
-    F3: FnOnce(&P, &mut Parser<'i, 't>, bool) -> Result<ColorComponent<R3>, ParseError<'i>>,
+    F1: FnOnce(
+        &ColorParser<'a, 'b>,
+        &mut Parser<'i, 't>,
+        bool,
+    ) -> Result<ColorComponent<R1>, ParseError<'i>>,
+    F2: FnOnce(
+        &ColorParser<'a, 'b>,
+        &mut Parser<'i, 't>,
+        bool,
+    ) -> Result<ColorComponent<R2>, ParseError<'i>>,
+    F3: FnOnce(
+        &ColorParser<'a, 'b>,
+        &mut Parser<'i, 't>,
+        bool,
+    ) -> Result<ColorComponent<R3>, ParseError<'i>>,
 {
     let r1 = f1(color_parser, input, true)?;
     let r2 = f2(color_parser, input, true)?;
@@ -407,6 +426,7 @@ where
 }
 
 /// Either a number or a percentage.
+#[derive(Clone, Copy, Debug)]
 pub enum NumberOrPercentage {
     /// `<number>`.
     Number {
@@ -432,7 +452,32 @@ impl NumberOrPercentage {
     }
 }
 
+impl ColorComponentType for NumberOrPercentage {
+    fn units() -> CalcUnits {
+        CalcUnits::PERCENTAGE
+    }
+
+    fn try_from_token(token: &Token) -> Result<Self, ()> {
+        Ok(match *token {
+            Token::Number { value, .. } => Self::Number { value },
+            Token::Percentage { unit_value, .. } => Self::Percentage { unit_value },
+            _ => {
+                return Err(());
+            },
+        })
+    }
+
+    fn try_from_leaf(leaf: &SpecifiedLeaf) -> Result<Self, ()> {
+        Ok(match *leaf {
+            SpecifiedLeaf::Percentage(unit_value) => Self::Percentage { unit_value },
+            SpecifiedLeaf::Number(value) => Self::Number { value },
+            _ => return Err(()),
+        })
+    }
+}
+
 /// Either an angle or a number.
+#[derive(Clone, Copy, Debug)]
 pub enum NumberOrAngle {
     /// `<number>`.
     Number {
@@ -457,45 +502,118 @@ impl NumberOrAngle {
     }
 }
 
-/// A trait that can be used to hook into how `cssparser` parses color
-/// components, with the intention of implementing more complicated behavior.
-///
-/// For example, this is used by Servo to support calc() in color.
-pub trait ColorParser<'i> {
-    /// The type that the parser will construct on a successful parse.
-    type Output: FromParsedColor;
-
-    /// Parse an `<angle>` or `<number>`.
-    ///
-    /// Returns the result in degrees.
-    fn parse_number_or_angle<'t>(
+impl ColorComponentType for NumberOrAngle {
+    fn units() -> CalcUnits {
+        CalcUnits::ANGLE
+    }
+
+    fn try_from_token(token: &Token) -> Result<Self, ()> {
+        Ok(match *token {
+            Token::Number { value, .. } => Self::Number { value },
+            Token::Dimension {
+                value, ref unit, ..
+            } => {
+                let degrees =
+                    SpecifiedAngle::parse_dimension(value, unit, /* from_calc = */ false)
+                        .map(|angle| angle.degrees())?;
+
+                NumberOrAngle::Angle { degrees }
+            },
+            _ => {
+                return Err(());
+            },
+        })
+    }
+
+    fn try_from_leaf(leaf: &SpecifiedLeaf) -> Result<Self, ()> {
+        Ok(match *leaf {
+            SpecifiedLeaf::Angle(angle) => Self::Angle {
+                degrees: angle.degrees(),
+            },
+            SpecifiedLeaf::Number(value) => Self::Number { value },
+            _ => return Err(()),
+        })
+    }
+}
+
+/// The raw f32 here is for <number>.
+impl ColorComponentType for f32 {
+    fn units() -> CalcUnits {
+        CalcUnits::empty()
+    }
+
+    fn try_from_token(token: &Token) -> Result<Self, ()> {
+        if let Token::Number { value, .. } = *token {
+            Ok(value)
+        } else {
+            Err(())
+        }
+    }
+
+    fn try_from_leaf(leaf: &SpecifiedLeaf) -> Result<Self, ()> {
+        if let SpecifiedLeaf::Number(value) = *leaf {
+            Ok(value)
+        } else {
+            Err(())
+        }
+    }
+}
+
+/// Used to parse the components of a color.
+pub struct ColorParser<'a, 'b: 'a> {
+    /// Parser context used for parsing the colors.
+    pub context: &'a ParserContext<'b>,
+}
+
+impl<'a, 'b: 'a> ColorParser<'a, 'b> {
+    /// Parse an `<number>` or `<angle>` value.
+    fn parse_number_or_angle<'i, 't>(
         &self,
         input: &mut Parser<'i, 't>,
         allow_none: bool,
-    ) -> Result<ColorComponent<NumberOrAngle>, ParseError<'i>>;
+    ) -> Result<ColorComponent<NumberOrAngle>, ParseError<'i>> {
+        ColorComponent::parse(self.context, input, allow_none)
+    }
 
     /// Parse a `<percentage>` value.
-    ///
-    /// Returns the result in a number from 0.0 to 1.0.
-    fn parse_percentage<'t>(
+    fn parse_percentage<'i, 't>(
         &self,
         input: &mut Parser<'i, 't>,
         allow_none: bool,
-    ) -> Result<ColorComponent<f32>, ParseError<'i>>;
+    ) -> Result<ColorComponent<f32>, ParseError<'i>> {
+        let location = input.current_source_location();
+
+        // We can use the [NumberOrPercentage] type here, because parsing it
+        // doesn't have any more overhead than just parsing a percentage on its
+        // own.
+        Ok(
+            match ColorComponent::<NumberOrPercentage>::parse(self.context, input, allow_none)? {
+                ColorComponent::None => ColorComponent::None,
+                ColorComponent::Value(NumberOrPercentage::Percentage { unit_value }) => {
+                    ColorComponent::Value(unit_value)
+                },
+                _ => return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError)),
+            },
+        )
+    }
 
     /// Parse a `<number>` value.
-    fn parse_number<'t>(
+    fn parse_number<'i, 't>(
         &self,
         input: &mut Parser<'i, 't>,
         allow_none: bool,
-    ) -> Result<ColorComponent<f32>, ParseError<'i>>;
+    ) -> Result<ColorComponent<f32>, ParseError<'i>> {
+        ColorComponent::parse(self.context, input, allow_none)
+    }
 
-    /// Parse a `<number>` value or a `<percentage>` value.
-    fn parse_number_or_percentage<'t>(
+    /// Parse a `<number>` or `<percentage>` value.
+    fn parse_number_or_percentage<'i, 't>(
         &self,
         input: &mut Parser<'i, 't>,
         allow_none: bool,
-    ) -> Result<ColorComponent<NumberOrPercentage>, ParseError<'i>>;
+    ) -> Result<ColorComponent<NumberOrPercentage>, ParseError<'i>> {
+        ColorComponent::parse(self.context, input, allow_none)
+    }
 }
 
 /// This trait is used by the [`ColorParser`] to construct colors of any type.
diff --git a/servo/components/style/context.rs b/servo/components/style/context.rs
index a2c020475b..8229721006 100644
--- a/servo/components/style/context.rs
+++ b/servo/components/style/context.rs
@@ -41,7 +41,6 @@ use style_traits::CSSPixel;
 use style_traits::DevicePixel;
 #[cfg(feature = "servo")]
 use style_traits::SpeculativePainter;
-use time;
 
 pub use selectors::matching::QuirksMode;
 
diff --git a/servo/components/style/custom_properties.rs b/servo/components/style/custom_properties.rs
index b6523dd489..766fe530d9 100644
--- a/servo/components/style/custom_properties.rs
+++ b/servo/components/style/custom_properties.rs
@@ -125,7 +125,12 @@ macro_rules! lnf_int_variable {
     }};
 }
 
-static CHROME_ENVIRONMENT_VARIABLES: [EnvironmentVariable; 8] = [
+static CHROME_ENVIRONMENT_VARIABLES: [EnvironmentVariable; 9] = [
+    lnf_int_variable!(
+        atom!("-moz-mac-titlebar-height"),
+        MacTitlebarHeight,
+        int_pixels
+    ),
     lnf_int_variable!(
         atom!("-moz-gtk-csd-titlebar-button-spacing"),
         TitlebarButtonSpacing,
diff --git a/servo/components/style/dom.rs b/servo/components/style/dom.rs
index 358d788845..ec99a796c1 100644
--- a/servo/components/style/dom.rs
+++ b/servo/components/style/dom.rs
@@ -14,12 +14,12 @@ use crate::context::{PostAnimationTasks, UpdateAnimationsTasks};
 use crate::data::ElementData;
 use crate::media_queries::Device;
 use crate::properties::{AnimationDeclarations, ComputedValues, PropertyDeclarationBlock};
-use crate::selector_parser::{AttrValue, CustomState, Lang, PseudoElement, SelectorImpl};
+use crate::selector_parser::{AttrValue, Lang, PseudoElement, SelectorImpl};
 use crate::shared_lock::{Locked, SharedRwLock};
 use crate::stylist::CascadeData;
 use crate::values::computed::Display;
 use crate::values::AtomIdent;
-use crate::WeakAtom;
+use crate::{LocalName, WeakAtom};
 use atomic_refcell::{AtomicRef, AtomicRefMut};
 use dom::ElementState;
 use selectors::matching::{ElementSelectorFlags, QuirksMode, VisitedHandlingMode};
@@ -511,11 +511,6 @@ pub trait TElement:
     /// Get this element's state, for non-tree-structural pseudos.
     fn state(&self) -> ElementState;
 
-    /// Returns whether this element's CustomStateSet contains a given state.
-    fn has_custom_state(&self, _state: &CustomState) -> bool {
-        false
-    }
-
     /// Returns whether this element has a `part` attribute.
     fn has_part_attr(&self) -> bool;
 
@@ -530,6 +525,11 @@ pub trait TElement:
     where
         F: FnMut(&AtomIdent);
 
+    /// Internal iterator for the classes of this element.
+    fn each_custom_state<F>(&self, callback: F)
+    where
+        F: FnMut(&AtomIdent);
+
     /// Internal iterator for the part names of this element.
     fn each_part<F>(&self, _callback: F)
     where
@@ -540,7 +540,7 @@ pub trait TElement:
     /// Internal iterator for the attribute names of this element.
     fn each_attr_name<F>(&self, callback: F)
     where
-        F: FnMut(&AtomIdent);
+        F: FnMut(&LocalName);
 
     /// Internal iterator for the part names that this element exports for a
     /// given part name.
@@ -906,7 +906,7 @@ pub trait TElement:
     fn has_selector_flags(&self, flags: ElementSelectorFlags) -> bool;
 
     /// Returns the search direction for relative selector invalidation, if it is on the search path.
-    fn relative_selector_search_direction(&self) -> Option<ElementSelectorFlags>;
+    fn relative_selector_search_direction(&self) -> ElementSelectorFlags;
 }
 
 /// TNode and TElement aren't Send because we want to be careful and explicit
diff --git a/servo/components/style/dom_apis.rs b/servo/components/style/dom_apis.rs
index cdc106e1ad..34ea73e5e6 100644
--- a/servo/components/style/dom_apis.rs
+++ b/servo/components/style/dom_apis.rs
@@ -368,7 +368,7 @@ fn collect_elements_with_id<E, Q, F>(
     }
 }
 
-fn has_attr<E>(element: E, local_name: &AtomIdent) -> bool
+fn has_attr<E>(element: E, local_name: &crate::LocalName) -> bool
 where
     E: TElement,
 {
@@ -396,7 +396,7 @@ where
     element.local_name() == &**chosen_name
 }
 
-fn get_attr_name(component: &Component<SelectorImpl>) -> Option<&AtomIdent> {
+fn get_attr_name(component: &Component<SelectorImpl>) -> Option<&crate::LocalName> {
     let (name, name_lower) = match component {
         Component::AttributeInNoNamespace { ref local_name, .. } => return Some(local_name),
         Component::AttributeInNoNamespaceExists {
@@ -512,7 +512,7 @@ where
 
 enum SimpleFilter<'a> {
     Class(&'a AtomIdent),
-    Attr(&'a AtomIdent),
+    Attr(&'a crate::LocalName),
     LocalName(&'a LocalName<SelectorImpl>),
 }
 
diff --git a/servo/components/style/driver.rs b/servo/components/style/driver.rs
index a2407cb209..59f401895a 100644
--- a/servo/components/style/driver.rs
+++ b/servo/components/style/driver.rs
@@ -13,9 +13,7 @@ use crate::dom::{SendNode, TElement, TNode};
 use crate::parallel;
 use crate::scoped_tls::ScopedTLS;
 use crate::traversal::{DomTraversal, PerLevelTraversalData, PreTraverseToken};
-use rayon;
 use std::collections::VecDeque;
-use time;
 
 #[cfg(feature = "servo")]
 fn should_report_statistics() -> bool {
@@ -36,14 +34,17 @@ fn report_statistics(_stats: &PerThreadTraversalStatistics) {
 fn report_statistics(stats: &PerThreadTraversalStatistics) {
     // This should only be called in the main thread, or it may be racy
     // to update the statistics in a global variable.
-    debug_assert!(unsafe { crate::gecko_bindings::bindings::Gecko_IsMainThread() });
-    let gecko_stats =
-        unsafe { &mut crate::gecko_bindings::structs::ServoTraversalStatistics_sSingleton };
-    gecko_stats.mElementsTraversed += stats.elements_traversed;
-    gecko_stats.mElementsStyled += stats.elements_styled;
-    gecko_stats.mElementsMatched += stats.elements_matched;
-    gecko_stats.mStylesShared += stats.styles_shared;
-    gecko_stats.mStylesReused += stats.styles_reused;
+    unsafe {
+        debug_assert!(crate::gecko_bindings::bindings::Gecko_IsMainThread());
+        let gecko_stats = std::ptr::addr_of_mut!(
+            crate::gecko_bindings::structs::ServoTraversalStatistics_sSingleton
+        );
+        (*gecko_stats).mElementsTraversed += stats.elements_traversed;
+        (*gecko_stats).mElementsStyled += stats.elements_styled;
+        (*gecko_stats).mElementsMatched += stats.elements_matched;
+        (*gecko_stats).mStylesShared += stats.styles_shared;
+        (*gecko_stats).mStylesReused += stats.styles_reused;
+    }
 }
 
 fn with_pool_in_place_scope<'scope>(
diff --git a/servo/components/style/gecko/arc_types.rs b/servo/components/style/gecko/arc_types.rs
index 24bf22d69a..420b86d332 100644
--- a/servo/components/style/gecko/arc_types.rs
+++ b/servo/components/style/gecko/arc_types.rs
@@ -16,7 +16,8 @@ use crate::stylesheets::keyframes_rule::Keyframe;
 use crate::stylesheets::{
     ContainerRule, CounterStyleRule, CssRules, DocumentRule, FontFaceRule, FontFeatureValuesRule,
     FontPaletteValuesRule, ImportRule, KeyframesRule, LayerBlockRule, LayerStatementRule,
-    MediaRule, NamespaceRule, PageRule, PropertyRule, StyleRule, StylesheetContents, SupportsRule,
+    MediaRule, NamespaceRule, PageRule, PropertyRule, ScopeRule, StartingStyleRule, StyleRule,
+    StylesheetContents, SupportsRule,
 };
 use servo_arc::Arc;
 
@@ -169,3 +170,13 @@ impl_simple_arc_ffi!(
     Servo_AnimationValue_AddRef,
     Servo_AnimationValue_Release
 );
+impl_simple_arc_ffi!(
+    ScopeRule,
+    Servo_ScopeRule_AddRef,
+    Servo_ScopeRule_Release
+);
+impl_simple_arc_ffi!(
+    StartingStyleRule,
+    Servo_StartingStyleRule_AddRef,
+    Servo_StartingStyleRule_Release
+);
diff --git a/servo/components/style/gecko/media_features.rs b/servo/components/style/gecko/media_features.rs
index 8de45d95c2..df1c5e464b 100644
--- a/servo/components/style/gecko/media_features.rs
+++ b/servo/components/style/gecko/media_features.rs
@@ -8,13 +8,14 @@ use crate::gecko_bindings::bindings;
 use crate::gecko_bindings::structs;
 use crate::gecko_bindings::structs::ScreenColorGamut;
 use crate::media_queries::{Device, MediaType};
-use crate::queries::condition::KleeneValue;
+use crate::parser::ParserContext;
 use crate::queries::feature::{AllowsRanges, Evaluator, FeatureFlags, QueryFeatureDescription};
 use crate::queries::values::Orientation;
 use crate::values::computed::{CSSPixelLength, Context, Ratio, Resolution};
 use crate::values::AtomString;
 use app_units::Au;
 use euclid::default::Size2D;
+use selectors::kleene_value::KleeneValue;
 
 fn device_size(device: &Device) -> Size2D<Au> {
     let mut width = 0;
@@ -286,16 +287,26 @@ fn eval_prefers_contrast(context: &Context, query_value: Option<PrefersContrast>
 pub enum ForcedColors {
     /// Page colors are not being forced.
     None,
+    /// Page colors would be forced in content.
+    #[parse(condition = "ParserContext::chrome_rules_enabled")]
+    Requested,
     /// Page colors are being forced.
     Active,
 }
 
+impl ForcedColors {
+    /// Returns whether forced-colors is active for this page.
+    pub fn is_active(self) -> bool {
+        matches!(self, Self::Active)
+    }
+}
+
 /// https://drafts.csswg.org/mediaqueries-5/#forced-colors
 fn eval_forced_colors(context: &Context, query_value: Option<ForcedColors>) -> bool {
-    let forced = !context.device().use_document_colors();
+    let forced = context.device().forced_colors();
     match query_value {
-        Some(query_value) => forced == (query_value == ForcedColors::Active),
-        None => forced,
+        Some(query_value) => query_value == forced,
+        None => forced != ForcedColors::None,
     }
 }
 
diff --git a/servo/components/style/gecko/media_queries.rs b/servo/components/style/gecko/media_queries.rs
index ef156ab380..ded66027f2 100644
--- a/servo/components/style/gecko/media_queries.rs
+++ b/servo/components/style/gecko/media_queries.rs
@@ -29,6 +29,8 @@ use std::sync::atomic::{AtomicBool, AtomicU32, AtomicUsize, Ordering};
 use std::{cmp, fmt};
 use style_traits::{CSSPixel, DevicePixel};
 
+use super::media_features::ForcedColors;
+
 /// The `Device` in Gecko wraps a pres context, has a default values computed,
 /// and contains all the viewport rule state.
 pub struct Device {
@@ -172,10 +174,9 @@ impl Device {
         Length::new(f32::from_bits(self.root_font_size.load(Ordering::Relaxed)))
     }
 
-    /// Set the font size of the root element (for rem)
-    pub fn set_root_font_size(&self, size: Length) {
-        self.root_font_size
-            .store(size.px().to_bits(), Ordering::Relaxed)
+    /// Set the font size of the root element (for rem), in zoom-independent CSS pixels.
+    pub fn set_root_font_size(&self, size: f32) {
+        self.root_font_size.store(size.to_bits(), Ordering::Relaxed)
     }
 
     /// Get the line height of the root element (for rlh)
@@ -186,10 +187,9 @@ impl Device {
         ))
     }
 
-    /// Set the line height of the root element (for rlh)
-    pub fn set_root_line_height(&self, size: Length) {
-        self.root_line_height
-            .store(size.px().to_bits(), Ordering::Relaxed);
+    /// Set the line height of the root element (for rlh), in zoom-independent CSS pixels.
+    pub fn set_root_line_height(&self, size: f32) {
+        self.root_line_height.store(size.to_bits(), Ordering::Relaxed);
     }
 
     /// The quirks mode of the document.
@@ -498,12 +498,27 @@ impl Device {
 
     /// Returns whether document colors are enabled.
     #[inline]
-    pub fn use_document_colors(&self) -> bool {
-        let doc = self.document();
-        if doc.mIsBeingUsedAsImage() {
-            return true;
+    pub fn forced_colors(&self) -> ForcedColors {
+        if self.document().mIsBeingUsedAsImage() {
+            // SVG images never force colors.
+            return ForcedColors::None
+        }
+        let prefs = self.pref_sheet_prefs();
+        if !prefs.mUseDocumentColors {
+            return ForcedColors::Active
+        }
+        // On Windows, having a high contrast theme also means that the OS is requesting the
+        // colors to be forced. This is mostly convenience for the front-end, which wants to
+        // reuse the forced-colors styles for chrome in this case as well, and it's a lot
+        // more convenient to use `(forced-colors)` than
+        // `(forced-colors) or ((-moz-platform: windows) and (prefers-contrast))`.
+        //
+        // TODO(emilio): We might want to factor in here the lwtheme attribute in the root element
+        // and so on.
+        if cfg!(target_os = "windows") && prefs.mUseAccessibilityTheme && prefs.mIsChrome {
+            return ForcedColors::Requested;
         }
-        self.pref_sheet_prefs().mUseDocumentColors
+        ForcedColors::None
     }
 
     /// Computes a system color and returns it as an nscolor.
diff --git a/servo/components/style/gecko/non_ts_pseudo_class_list.rs b/servo/components/style/gecko/non_ts_pseudo_class_list.rs
index cc7495dd9c..f628c77ad5 100644
--- a/servo/components/style/gecko/non_ts_pseudo_class_list.rs
+++ b/servo/components/style/gecko/non_ts_pseudo_class_list.rs
@@ -98,7 +98,6 @@ macro_rules! apply_non_ts_list {
                 // media query results are more expensive than document state changes. So for now
                 // making them pseudo-classes is probably the right trade-off.
                 ("-moz-is-html", MozIsHTML, _, PSEUDO_CLASS_ENABLED_IN_UA_SHEETS),
-                ("-moz-lwtheme", MozLWTheme, _, PSEUDO_CLASS_ENABLED_IN_UA_SHEETS_AND_CHROME),
                 ("-moz-window-inactive", MozWindowInactive, _, _),
             ]
         }
diff --git a/servo/components/style/gecko/pseudo_element.rs b/servo/components/style/gecko/pseudo_element.rs
index 3bcd873455..f0e79a8acd 100644
--- a/servo/components/style/gecko/pseudo_element.rs
+++ b/servo/components/style/gecko/pseudo_element.rs
@@ -159,6 +159,11 @@ impl PseudoElement {
         matches!(*self, Self::Highlight(_))
     }
 
+    /// Whether this pseudo-element is the ::target-text pseudo.
+    #[inline]
+    pub fn is_target_text(&self) -> bool {
+        *self == PseudoElement::TargetText
+    }
     /// Whether this pseudo-element supports user action selectors.
     pub fn supports_user_action_state(&self) -> bool {
         (self.flags() & structs::CSS_PSEUDO_ELEMENT_SUPPORTS_USER_ACTION_STATE) != 0
@@ -168,6 +173,7 @@ impl PseudoElement {
     pub fn enabled_in_content(&self) -> bool {
         match *self {
             Self::Highlight(..) => pref!("dom.customHighlightAPI.enabled"),
+            Self::TargetText => pref!("dom.text_fragments.enabled"),
             Self::SliderFill | Self::SliderTrack | Self::SliderThumb => {
                 pref!("layout.css.modern-range-pseudos.enabled")
             },
diff --git a/servo/components/style/gecko/selector_parser.rs b/servo/components/style/gecko/selector_parser.rs
index 203e6a3609..100bb45e81 100644
--- a/servo/components/style/gecko/selector_parser.rs
+++ b/servo/components/style/gecko/selector_parser.rs
@@ -196,7 +196,6 @@ impl NonTSPseudoClass {
                 None => DocumentState::empty(),
             },
             NonTSPseudoClass::MozWindowInactive => DocumentState::WINDOW_INACTIVE,
-            NonTSPseudoClass::MozLWTheme => DocumentState::LWTHEME,
             _ => DocumentState::empty(),
         }
     }
@@ -214,11 +213,10 @@ impl NonTSPseudoClass {
                       NonTSPseudoClass::MozNativeAnonymous |
                       // :-moz-placeholder is parsed but never matches.
                       NonTSPseudoClass::MozPlaceholder |
-                      // :-moz-is-html, :-moz-lwtheme, :-moz-locale-dir and :-moz-window-inactive
+                      // :-moz-is-html, :-moz-locale-dir and :-moz-window-inactive
                       // depend only on the state of the document, which is invariant across all
                       // elements involved in a given style cache.
                       NonTSPseudoClass::MozIsHTML |
-                      NonTSPseudoClass::MozLWTheme |
                       NonTSPseudoClass::MozLocaleDir(_) |
                       NonTSPseudoClass::MozWindowInactive
             )
diff --git a/servo/components/style/gecko/snapshot.rs b/servo/components/style/gecko/snapshot.rs
index 2ff04406ac..8f6eb120d5 100644
--- a/servo/components/style/gecko/snapshot.rs
+++ b/servo/components/style/gecko/snapshot.rs
@@ -171,4 +171,33 @@ impl ElementSnapshot for GeckoElementSnapshot {
             Some(AtomString(unsafe { Atom::from_addrefed(ptr) }))
         }
     }
+
+    /// Returns true if the snapshot has stored state for custom states
+    #[inline]
+    fn has_custom_states(&self) -> bool {
+        self.has_any(Flags::CustomState)
+    }
+
+    /// Returns true if the snapshot has a given CustomState
+    #[inline]
+    fn has_custom_state(&self, state: &AtomIdent) -> bool {
+        unsafe {
+            self.mCustomStates.iter().any(|setstate| {
+                AtomIdent::with(setstate.mRawPtr, |setstate| state == setstate)
+            })
+        }
+    }
+
+    #[inline]
+    fn each_custom_state<F>(&self, mut callback: F)
+    where
+        F: FnMut(&AtomIdent),
+    {
+        unsafe {
+            for atom in self.mCustomStates.iter() {
+                AtomIdent::with(atom.mRawPtr, &mut callback)
+            }
+        }
+    }
+
 }
diff --git a/servo/components/style/gecko/url.rs b/servo/components/style/gecko/url.rs
index 7fe32acc20..fa8d22adb6 100644
--- a/servo/components/style/gecko/url.rs
+++ b/servo/components/style/gecko/url.rs
@@ -18,7 +18,7 @@ use std::fmt::{self, Write};
 use std::mem::ManuallyDrop;
 use std::sync::RwLock;
 use style_traits::{CssWriter, ParseError, ToCss};
-use to_shmem::{self, SharedMemoryBuilder, ToShmem};
+use to_shmem::{SharedMemoryBuilder, ToShmem};
 
 /// A CSS url() value for gecko.
 #[derive(Clone, Debug, PartialEq, SpecifiedValueInfo, ToCss, ToShmem)]
diff --git a/servo/components/style/gecko/wrapper.rs b/servo/components/style/gecko/wrapper.rs
index 43cf6e7941..eab968149c 100644
--- a/servo/components/style/gecko/wrapper.rs
+++ b/servo/components/style/gecko/wrapper.rs
@@ -19,7 +19,7 @@ use crate::bloom::each_relevant_element_hash;
 use crate::context::{PostAnimationTasks, QuirksMode, SharedStyleContext, UpdateAnimationsTasks};
 use crate::data::ElementData;
 use crate::dom::{LayoutIterator, NodeInfo, OpaqueNode, TDocument, TElement, TNode, TShadowRoot};
-use crate::gecko::selector_parser::{CustomState, NonTSPseudoClass, PseudoElement, SelectorImpl};
+use crate::gecko::selector_parser::{NonTSPseudoClass, PseudoElement, SelectorImpl};
 use crate::gecko::snapshot_helpers;
 use crate::gecko_bindings::bindings;
 use crate::gecko_bindings::bindings::Gecko_ElementHasAnimations;
@@ -889,7 +889,11 @@ impl<'le> GeckoElement<'le> {
             AnimationValue::from_computed_values(property_declaration_id, before_change_style);
         let to = AnimationValue::from_computed_values(property_declaration_id, after_change_style);
 
-        debug_assert_eq!(to.is_some(), from.is_some());
+        // If the declaration contains a custom property and getComputedValue was previously called
+        // before that custom property was defined, `from` will be `None` here.
+        debug_assert!(
+            to.is_some() == from.is_some() || matches!(to, Some(AnimationValue::Custom(..)))
+        );
 
         from != to
     }
@@ -1237,20 +1241,6 @@ impl<'le> TElement for GeckoElement<'le> {
     }
 
     #[inline]
-    fn has_custom_state(&self, state: &CustomState) -> bool {
-        if !self.is_html_element() {
-            return false;
-        }
-        let check_state_ptr: *const nsAtom = state.0.as_ptr();
-        self.extended_slots().map_or(false, |slot| {
-            (&slot.mCustomStates).iter().any(|setstate| {
-                let setstate_ptr: *const nsAtom = setstate.mRawPtr;
-                setstate_ptr == check_state_ptr
-            })
-        })
-    }
-
-    #[inline]
     fn has_part_attr(&self) -> bool {
         self.as_node()
             .get_bool_flag(nsINode_BooleanFlag::ElementHasPart)
@@ -1292,6 +1282,20 @@ impl<'le> TElement for GeckoElement<'le> {
     }
 
     #[inline]
+    fn each_custom_state<F>(&self, mut callback: F)
+    where
+        F: FnMut(&AtomIdent),
+    {
+        if let Some(slots) = self.extended_slots() {
+            unsafe {
+                for atom in slots.mCustomStates.iter() {
+                    AtomIdent::with(atom.mRawPtr, &mut callback)
+                }
+            }
+        }
+    }
+
+    #[inline]
     fn each_exported_part<F>(&self, name: &AtomIdent, callback: F)
     where
         F: FnMut(&AtomIdent),
@@ -1551,14 +1555,13 @@ impl<'le> TElement for GeckoElement<'le> {
 
         let mut transitions_to_keep = PropertyDeclarationIdSet::default();
         for transition_property in after_change_style.transition_properties() {
-            let physical_longhand = PropertyDeclarationId::Longhand(
-                transition_property
-                    .longhand_id
-                    .to_physical(after_change_style.writing_mode),
-            );
-            transitions_to_keep.insert(physical_longhand);
+            let physical_property = transition_property
+                .property
+                .as_borrowed()
+                .to_physical(after_change_style.writing_mode);
+            transitions_to_keep.insert(physical_property);
             if self.needs_transitions_update_per_property(
-                physical_longhand,
+                physical_property,
                 after_change_ui_style
                     .transition_combined_duration_at(transition_property.index)
                     .seconds(),
@@ -1791,17 +1794,17 @@ impl<'le> TElement for GeckoElement<'le> {
         self.as_node().selector_flags() & node_flags == node_flags
     }
 
-    fn relative_selector_search_direction(&self) -> Option<ElementSelectorFlags> {
+    fn relative_selector_search_direction(&self) -> ElementSelectorFlags {
         use crate::gecko_bindings::structs::NodeSelectorFlags;
         let flags = self.as_node().selector_flags();
         if (flags & NodeSelectorFlags::RelativeSelectorSearchDirectionAncestorSibling.0) != 0 {
-            Some(ElementSelectorFlags::RELATIVE_SELECTOR_SEARCH_DIRECTION_ANCESTOR_SIBLING)
+            ElementSelectorFlags::RELATIVE_SELECTOR_SEARCH_DIRECTION_ANCESTOR_SIBLING
         } else if (flags & NodeSelectorFlags::RelativeSelectorSearchDirectionAncestor.0) != 0 {
-            Some(ElementSelectorFlags::RELATIVE_SELECTOR_SEARCH_DIRECTION_ANCESTOR)
+            ElementSelectorFlags::RELATIVE_SELECTOR_SEARCH_DIRECTION_ANCESTOR
         } else if (flags & NodeSelectorFlags::RelativeSelectorSearchDirectionSibling.0) != 0 {
-            Some(ElementSelectorFlags::RELATIVE_SELECTOR_SEARCH_DIRECTION_SIBLING)
+            ElementSelectorFlags::RELATIVE_SELECTOR_SEARCH_DIRECTION_SIBLING
         } else {
-            None
+            ElementSelectorFlags::empty()
         }
     }
 }
@@ -2042,15 +2045,14 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
             NonTSPseudoClass::MozAutofillPreview |
             NonTSPseudoClass::MozRevealed |
             NonTSPseudoClass::MozValueEmpty => self.state().intersects(pseudo_class.state_flag()),
-            // TODO: This applying only to HTML elements is weird.
             NonTSPseudoClass::Dir(ref dir) => {
-                self.is_html_element() && self.state().intersects(dir.element_state())
+                self.state().intersects(dir.element_state())
             },
             NonTSPseudoClass::AnyLink => self.is_link(),
             NonTSPseudoClass::Link => {
                 self.is_link() && context.visited_handling().matches_unvisited()
             },
-            NonTSPseudoClass::CustomState(ref state) => self.has_custom_state(state),
+            NonTSPseudoClass::CustomState(ref state) => self.has_custom_state(&state.0),
             NonTSPseudoClass::Visited => {
                 self.is_link() && context.visited_handling().matches_visited()
             },
@@ -2101,7 +2103,6 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
                 bindings::Gecko_IsSelectListBox(self.0)
             },
             NonTSPseudoClass::MozIsHTML => self.as_node().owner_doc().is_html_document(),
-            NonTSPseudoClass::MozLWTheme |
             NonTSPseudoClass::MozLocaleDir(..) |
             NonTSPseudoClass::MozWindowInactive => {
                 let state_bit = pseudo_class.document_state_flag();
@@ -2186,6 +2187,20 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
     }
 
     #[inline]
+    fn has_custom_state(&self, state: &AtomIdent) -> bool {
+        if !self.is_html_element() {
+            return false;
+        }
+        let check_state_ptr: *const nsAtom = state.as_ptr();
+        self.extended_slots().map_or(false, |slot| {
+            (&slot.mCustomStates).iter().any(|setstate| {
+                let setstate_ptr: *const nsAtom = setstate.mRawPtr;
+                setstate_ptr == check_state_ptr
+            })
+        })
+    }
+
+    #[inline]
     fn is_html_element_in_html_document(&self) -> bool {
         self.is_html_element() && self.as_node().owner_doc().is_html_document()
     }
diff --git a/servo/components/style/gecko_bindings/sugar/ns_style_auto_array.rs b/servo/components/style/gecko_bindings/sugar/ns_style_auto_array.rs
index b5772a6c77..350d578001 100644
--- a/servo/components/style/gecko_bindings/sugar/ns_style_auto_array.rs
+++ b/servo/components/style/gecko_bindings/sugar/ns_style_auto_array.rs
@@ -11,7 +11,7 @@ use crate::gecko_bindings::bindings::Gecko_EnsureStyleViewTimelineArrayLength;
 use crate::gecko_bindings::structs::nsStyleAutoArray;
 use crate::gecko_bindings::structs::{StyleAnimation, StyleTransition};
 use crate::gecko_bindings::structs::{StyleScrollTimeline, StyleViewTimeline};
-use std::iter::{once, Chain, IntoIterator, Once};
+use std::iter::{once, Chain, Once};
 use std::ops::{Index, IndexMut};
 use std::slice::{Iter, IterMut};
 
diff --git a/servo/components/style/gecko_string_cache/mod.rs b/servo/components/style/gecko_string_cache/mod.rs
index 79a5d46525..3640b61d11 100644
--- a/servo/components/style/gecko_string_cache/mod.rs
+++ b/servo/components/style/gecko_string_cache/mod.rs
@@ -28,7 +28,7 @@ use std::num::NonZeroUsize;
 use std::ops::Deref;
 use std::{slice, str};
 use style_traits::SpecifiedValueInfo;
-use to_shmem::{self, SharedMemoryBuilder, ToShmem};
+use to_shmem::{SharedMemoryBuilder, ToShmem};
 
 #[macro_use]
 #[allow(improper_ctypes, non_camel_case_types, missing_docs)]
diff --git a/servo/components/style/global_style_data.rs b/servo/components/style/global_style_data.rs
index 38d72b2c74..d6e49e7da6 100644
--- a/servo/components/style/global_style_data.rs
+++ b/servo/components/style/global_style_data.rs
@@ -10,9 +10,7 @@ use crate::gecko_bindings::bindings;
 use crate::parallel::STYLE_THREAD_STACK_SIZE_KB;
 use crate::shared_lock::SharedRwLock;
 use crate::thread_state;
-use gecko_profiler;
 use parking_lot::{Mutex, RwLock, RwLockReadGuard};
-use rayon;
 #[cfg(unix)]
 use std::os::unix::thread::{JoinHandleExt, RawPthread};
 #[cfg(windows)]
diff --git a/servo/components/style/invalidation/element/element_wrapper.rs b/servo/components/style/invalidation/element/element_wrapper.rs
index e17afd7774..9a39b7d5a0 100644
--- a/servo/components/style/invalidation/element/element_wrapper.rs
+++ b/servo/components/style/invalidation/element/element_wrapper.rs
@@ -73,6 +73,18 @@ pub trait ElementSnapshot: Sized {
     where
         F: FnMut(&AtomIdent);
 
+
+    /// If this snapshot contains CustomStateSet information.
+    fn has_custom_states(&self) -> bool;
+
+    /// A callback that should be called for each CustomState of the snapshot.
+    fn has_custom_state(&self, state: &AtomIdent) -> bool;
+
+    /// A callback that should be called for each CustomState of the snapshot.
+    fn each_custom_state<F>(&self, callback: F)
+    where
+        F: FnMut(&AtomIdent);
+
     /// The `xml:lang=""` or `lang=""` attribute value per this snapshot.
     fn lang_attr(&self) -> Option<AttrValue>;
 }
@@ -213,6 +225,11 @@ where
                     .match_element_lang(Some(self.get_lang()), lang_arg);
             },
 
+            // CustomStateSet should match against the snapshot before element
+            NonTSPseudoClass::CustomState(ref state) => {
+                return self.has_custom_state(&state.0)
+            },
+
             _ => {},
         }
 
@@ -357,6 +374,13 @@ where
         }
     }
 
+    fn has_custom_state(&self, state: &AtomIdent) -> bool {
+        match self.snapshot() {
+            Some(snapshot) if snapshot.has_custom_states() => snapshot.has_custom_state(state),
+            _ => self.element.has_custom_state(state),
+        }
+    }
+
     fn is_empty(&self) -> bool {
         self.element.is_empty()
     }
diff --git a/servo/components/style/invalidation/element/invalidation_map.rs b/servo/components/style/invalidation/element/invalidation_map.rs
index cb03862740..f42f542dd2 100644
--- a/servo/components/style/invalidation/element/invalidation_map.rs
+++ b/servo/components/style/invalidation/element/invalidation_map.rs
@@ -10,6 +10,7 @@ use crate::selector_map::{
 };
 use crate::selector_parser::{NonTSPseudoClass, SelectorImpl};
 use crate::AllocErr;
+use crate::values::AtomIdent;
 use crate::{Atom, LocalName, Namespace, ShrinkIfNeeded};
 use dom::{DocumentState, ElementState};
 use selectors::attr::NamespaceConstraint;
@@ -259,6 +260,8 @@ pub type IdOrClassDependencyMap = MaybeCaseInsensitiveHashMap<Atom, SmallVec<[De
 pub type StateDependencyMap = SelectorMap<StateDependency>;
 /// Dependency mapping for local names.
 pub type LocalNameDependencyMap = PrecomputedHashMap<LocalName, SmallVec<[Dependency; 1]>>;
+/// Dependency mapping for customstates
+pub type CustomStateDependencyMap = PrecomputedHashMap<AtomIdent, SmallVec<[Dependency; 1]>>;
 
 /// A map where we store invalidations.
 ///
@@ -282,6 +285,8 @@ pub struct InvalidationMap {
     pub document_state_selectors: Vec<DocumentStateDependency>,
     /// A map of other attribute affecting selectors.
     pub other_attribute_affecting_selectors: LocalNameDependencyMap,
+    /// A map of CSS custom states
+    pub custom_state_affecting_selectors: CustomStateDependencyMap,
 }
 
 /// Tree-structural pseudoclasses that we care about for (Relative selector) invalidation.
@@ -383,6 +388,7 @@ impl InvalidationMap {
             state_affecting_selectors: StateDependencyMap::new(),
             document_state_selectors: Vec::new(),
             other_attribute_affecting_selectors: LocalNameDependencyMap::default(),
+            custom_state_affecting_selectors: CustomStateDependencyMap::default(),
         }
     }
 
@@ -398,6 +404,9 @@ impl InvalidationMap {
                 .fold(0, |accum, (_, ref v)| accum + v.len()) +
             self.class_to_selector
                 .iter()
+                .fold(0, |accum, (_, ref v)| accum + v.len()) +
+            self.custom_state_affecting_selectors
+                .iter()
                 .fold(0, |accum, (_, ref v)| accum + v.len())
     }
 
@@ -408,6 +417,7 @@ impl InvalidationMap {
         self.state_affecting_selectors.clear();
         self.document_state_selectors.clear();
         self.other_attribute_affecting_selectors.clear();
+        self.custom_state_affecting_selectors.clear();
     }
 
     /// Shrink the capacity of hash maps if needed.
@@ -416,6 +426,7 @@ impl InvalidationMap {
         self.id_to_selector.shrink_if_needed();
         self.state_affecting_selectors.shrink_if_needed();
         self.other_attribute_affecting_selectors.shrink_if_needed();
+        self.custom_state_affecting_selectors.shrink_if_needed();
     }
 }
 
@@ -489,6 +500,7 @@ trait Collector {
     fn class_map(&mut self) -> &mut IdOrClassDependencyMap;
     fn state_map(&mut self) -> &mut StateDependencyMap;
     fn attribute_map(&mut self) -> &mut LocalNameDependencyMap;
+    fn custom_state_map(&mut self) -> &mut LocalNameDependencyMap;
     fn update_states(&mut self, element_state: ElementState, document_state: DocumentState);
 
     // In normal invalidations, type-based dependencies don't need to be explicitly tracked;
@@ -551,6 +563,16 @@ fn add_attr_dependency<C: Collector>(name: LocalName, collector: &mut C) -> Resu
     add_local_name(name, dependency, map)
 }
 
+fn add_custom_state_dependency<C: Collector>(name: AtomIdent, collector: &mut C) -> Result<(), AllocErr> {
+    let dependency = collector.dependency();
+    let map = collector.custom_state_map();
+    map.try_reserve(1)?;
+    let vec = map.entry(name).or_default();
+    vec.try_reserve(1)?;
+    vec.push(dependency);
+    Ok(())
+}
+
 fn add_local_name(
     name: LocalName,
     dependency: Dependency,
@@ -576,6 +598,9 @@ fn on_pseudo_class<C: Collector>(pc: &NonTSPseudoClass, collector: &mut C) -> Re
             return add_attr_dependency(local_name!("size"), collector);
         },
         NonTSPseudoClass::Lang(..) => local_name!("lang"),
+        NonTSPseudoClass::CustomState(ref name) => {
+            return add_custom_state_dependency(name.0.clone(), collector);
+        },
         _ => return Ok(()),
     };
 
@@ -702,6 +727,10 @@ impl<'a> Collector for SelectorDependencyCollector<'a> {
         self.compound_state.element_state |= element_state;
         *self.document_state |= document_state;
     }
+
+    fn custom_state_map(&mut self) -> &mut CustomStateDependencyMap {
+        &mut self.map.custom_state_affecting_selectors
+    }
 }
 
 impl<'a> SelectorDependencyCollector<'a> {
@@ -1074,6 +1103,10 @@ impl<'a> Collector for RelativeSelectorDependencyCollector<'a> {
         &mut self.map.map.other_attribute_affecting_selectors
     }
 
+    fn custom_state_map(&mut self) -> &mut CustomStateDependencyMap {
+        &mut self.map.map.custom_state_affecting_selectors
+    }
+
     fn update_states(&mut self, element_state: ElementState, document_state: DocumentState) {
         self.compound_state.state.element_state |= element_state;
         *self.document_state |= document_state;
@@ -1255,6 +1288,10 @@ impl<'a, 'b> Collector for RelativeSelectorInnerDependencyCollector<'a, 'b> {
         &mut self.map.map.other_attribute_affecting_selectors
     }
 
+    fn custom_state_map(&mut self) -> &mut CustomStateDependencyMap {
+        &mut self.map.map.custom_state_affecting_selectors
+    }
+
     fn update_states(&mut self, element_state: ElementState, document_state: DocumentState) {
         self.compound_state.state.element_state |= element_state;
         *self.document_state |= document_state;
diff --git a/servo/components/style/invalidation/element/relative_selector.rs b/servo/components/style/invalidation/element/relative_selector.rs
index ccb48e349f..41222304be 100644
--- a/servo/components/style/invalidation/element/relative_selector.rs
+++ b/servo/components/style/invalidation/element/relative_selector.rs
@@ -53,12 +53,12 @@ impl DomMutationOperation {
     fn accept<E: TElement>(&self, d: &Dependency, e: E) -> bool {
         match self {
             Self::Insert | Self::Append | Self::Remove => {
-                e.relative_selector_search_direction().is_some()
+                !e.relative_selector_search_direction().is_empty()
             },
             // `:has(+ .a + .b)` with `.anchor + .a + .remove + .b` - `.a` would be present
             // in the search path.
             Self::SideEffectPrevSibling => {
-                e.relative_selector_search_direction().is_some() &&
+                !e.relative_selector_search_direction().is_empty() &&
                     d.right_combinator_is_next_sibling()
             },
             // If an element is being removed and would cause next-sibling match to happen,
@@ -499,6 +499,19 @@ where
             },
             None => (),
         });
+        element.each_custom_state(|v| {
+            match map.map.custom_state_affecting_selectors.get(v) {
+                Some(v) => {
+                    for dependency in v {
+                        if !operation.accept(dependency, element) {
+                            continue;
+                        }
+                        self.add_dependency(dependency, element, scope);
+                    }
+                },
+                None => (),
+            }
+        });
         element.each_attr_name(
             |v| match map.map.other_attribute_affecting_selectors.get(v) {
                 Some(v) => {
@@ -782,11 +795,7 @@ where
 
     /// Is this element in the direction of the given relative selector search path?
     fn in_search_direction(element: &E, desired: ElementSelectorFlags) -> bool {
-        if let Some(direction) = element.relative_selector_search_direction() {
-            direction.intersects(desired)
-        } else {
-            false
-        }
+        element.relative_selector_search_direction().intersects(desired)
     }
 
     /// Handle a potential relative selector anchor.
@@ -1145,7 +1154,7 @@ where
         dep: &'a Dependency,
     ) {
         debug_assert!(dep.parent.is_some(), "Orphaned inners selector?");
-        if element.relative_selector_search_direction().is_none() {
+        if element.relative_selector_search_direction().is_empty() {
             return;
         }
         self.invalidations.push((
diff --git a/servo/components/style/invalidation/element/state_and_attributes.rs b/servo/components/style/invalidation/element/state_and_attributes.rs
index 1c58cddf1e..d5f0723d66 100644
--- a/servo/components/style/invalidation/element/state_and_attributes.rs
+++ b/servo/components/style/invalidation/element/state_and_attributes.rs
@@ -19,11 +19,12 @@ use crate::selector_map::SelectorMap;
 use crate::selector_parser::Snapshot;
 use crate::stylesheets::origin::OriginSet;
 use crate::{Atom, WeakAtom};
+use crate::values::AtomIdent;
 use dom::ElementState;
 use selectors::attr::CaseSensitivity;
+use selectors::kleene_value::KleeneValue;
 use selectors::matching::{
-    matches_selector, MatchingContext, MatchingForInvalidation, MatchingMode, NeedsSelectorFlags,
-    SelectorCaches, VisitedHandlingMode,
+    matches_selector_kleene, MatchingContext, MatchingForInvalidation, MatchingMode, NeedsSelectorFlags, SelectorCaches, VisitedHandlingMode
 };
 use smallvec::SmallVec;
 
@@ -41,6 +42,8 @@ where
     added_id: Option<&'a WeakAtom>,
     classes_removed: &'a SmallVec<[Atom; 8]>,
     classes_added: &'a SmallVec<[Atom; 8]>,
+    custom_states_removed: &'a SmallVec<[AtomIdent; 8]>,
+    custom_states_added: &'a SmallVec<[AtomIdent; 8]>,
     state_changes: ElementState,
     descendant_invalidations: &'a mut DescendantInvalidationLists<'selectors>,
     sibling_invalidations: &'a mut InvalidationVector<'selectors>,
@@ -97,23 +100,25 @@ where
     E: TElement,
     W: selectors::Element<Impl = E::Impl>,
 {
-    let matches_now = matches_selector(
-        &dependency.selector,
-        dependency.selector_offset,
-        None,
-        element,
-        context,
-    );
+    context.for_invalidation_comparison(|context| {
+        let matches_now = matches_selector_kleene(
+            &dependency.selector,
+            dependency.selector_offset,
+            None,
+            element,
+            context,
+        );
 
-    let matched_then = matches_selector(
-        &dependency.selector,
-        dependency.selector_offset,
-        None,
-        wrapper,
-        context,
-    );
+        let matched_then = matches_selector_kleene(
+            &dependency.selector,
+            dependency.selector_offset,
+            None,
+            wrapper,
+            context,
+        );
 
-    matched_then != matches_now
+        matched_then != matches_now || matches_now == KleeneValue::Unknown
+    })
 }
 
 /// Whether we should process the descendants of a given element for style
@@ -243,7 +248,7 @@ where
             return false;
         };
 
-        if !snapshot.has_attrs() && state_changes.is_empty() {
+        if !snapshot.has_attrs() && !snapshot.has_custom_states() && state_changes.is_empty() {
             return false;
         }
 
@@ -264,6 +269,21 @@ where
             })
         }
 
+        let mut custom_states_removed = SmallVec::<[AtomIdent; 8]>::new();
+        let mut custom_states_added = SmallVec::<[AtomIdent; 8]>::new();
+        if snapshot.has_custom_states() {
+            snapshot.each_custom_state(|s| {
+                if !element.has_custom_state(s) {
+                    custom_states_removed.push(s.clone())
+                }
+            });
+            element.each_custom_state(|s| {
+                if !snapshot.has_custom_state(s) {
+                    custom_states_added.push(s.clone())
+                }
+            })
+        }
+
         let mut id_removed = None;
         let mut id_added = None;
         if snapshot.id_changed() {
@@ -326,6 +346,8 @@ where
                 added_id: id_added,
                 classes_removed: &classes_removed,
                 classes_added: &classes_added,
+                custom_states_removed: &custom_states_removed,
+                custom_states_added: &custom_states_added,
                 descendant_invalidations,
                 sibling_invalidations,
                 invalidates_self: false,
@@ -443,6 +465,14 @@ where
             }
         }
 
+        for state in self.custom_states_added.iter().chain(self.custom_states_removed.iter()) {
+            if let Some(deps) = map.custom_state_affecting_selectors.get(state) {
+                for dep in deps {
+                    self.scan_dependency(dep);
+                }
+            }
+        }
+
         self.snapshot.each_attr_changed(|attribute| {
             if let Some(deps) = map.other_attribute_affecting_selectors.get(attribute) {
                 for dep in deps {
diff --git a/servo/components/style/invalidation/stylesheets.rs b/servo/components/style/invalidation/stylesheets.rs
index d845897aa4..48ef8c1b5d 100644
--- a/servo/components/style/invalidation/stylesheets.rs
+++ b/servo/components/style/invalidation/stylesheets.rs
@@ -616,7 +616,7 @@ impl StylesheetInvalidationSet {
                 return self.invalidate_fully();
             },
             Document(..) | Import(..) | Media(..) | Supports(..) | Container(..) |
-            LayerBlock(..) => {
+            LayerBlock(..) | StartingStyle(..) => {
                 // Do nothing, relevant nested rules are visited as part of rule iteration.
             },
             FontFace(..) => {
@@ -646,6 +646,11 @@ impl StylesheetInvalidationSet {
                 debug!(" > Found unsupported rule, marking the whole subtree invalid.");
                 self.invalidate_fully();
             },
+            Scope(..) => {
+                // Addition/removal of @scope requires re-evaluation of scope proximity to properly
+                // figure out the styling order.
+                self.invalidate_fully();
+            },
         }
     }
 }
diff --git a/servo/components/style/matching.rs b/servo/components/style/matching.rs
index 646d08a9e3..e9d754aa10 100644
--- a/servo/components/style/matching.rs
+++ b/servo/components/style/matching.rs
@@ -934,7 +934,8 @@ pub trait MatchMethods: TElement {
             if old_font_size != Some(new_font_size) {
                 if is_root {
                     debug_assert!(self.owner_doc_matches_for_testing(device));
-                    device.set_root_font_size(new_font_size.computed_size().into());
+                    let size = new_font_size.computed_size();
+                    device.set_root_font_size(new_primary_style.effective_zoom.unzoom(size.px()));
                     if device.used_root_font_size() {
                         // If the root font-size changed since last time, and something
                         // in the document did use rem units, ensure we recascade the
@@ -954,7 +955,8 @@ pub trait MatchMethods: TElement {
                 }
             }
 
-            // For line-height, we want the fully resolved value, as `normal` also depends on other font properties.
+            // For line-height, we want the fully resolved value, as `normal` also depends on other
+            // font properties.
             let new_line_height = device
                 .calc_line_height(
                     &new_primary_style.get_font(),
@@ -968,14 +970,12 @@ pub trait MatchMethods: TElement {
                     .0
             });
 
-            if restyle_requirement != ChildRestyleRequirement::MustMatchDescendants &&
-                old_line_height != Some(new_line_height)
-            {
+            if old_line_height != Some(new_line_height) {
                 if is_root {
                     debug_assert!(self.owner_doc_matches_for_testing(device));
-                    device.set_root_line_height(new_line_height.into());
+                    device.set_root_line_height(new_primary_style.effective_zoom.unzoom(new_line_height.px()));
                     if device.used_root_line_height() {
-                        restyle_requirement = ChildRestyleRequirement::MustCascadeDescendants;
+                        restyle_requirement = std::cmp::max(restyle_requirement, ChildRestyleRequirement::MustCascadeDescendants);
                     }
                 }
 
diff --git a/servo/components/style/media_queries/media_list.rs b/servo/components/style/media_queries/media_list.rs
index 3c2ba9ee5c..7cbbeb5e3e 100644
--- a/servo/components/style/media_queries/media_list.rs
+++ b/servo/components/style/media_queries/media_list.rs
@@ -10,10 +10,10 @@ use super::{Device, MediaQuery, Qualifier};
 use crate::context::QuirksMode;
 use crate::error_reporting::ContextualParseError;
 use crate::parser::ParserContext;
-use crate::queries::condition::KleeneValue;
 use crate::values::computed;
 use cssparser::{Delimiter, Parser};
 use cssparser::{ParserInput, Token};
+use selectors::kleene_value::KleeneValue;
 
 /// A type that encapsulates a media query list.
 #[derive(Clone, MallocSizeOf, ToCss, ToShmem)]
diff --git a/servo/components/style/parallel.rs b/servo/components/style/parallel.rs
index 0b2ccf46d1..0e1c509ab7 100644
--- a/servo/components/style/parallel.rs
+++ b/servo/components/style/parallel.rs
@@ -26,7 +26,6 @@ use crate::context::{StyleContext, ThreadLocalStyleContext};
 use crate::dom::{OpaqueNode, SendNode, TElement};
 use crate::scoped_tls::ScopedTLS;
 use crate::traversal::{DomTraversal, PerLevelTraversalData};
-use rayon;
 use std::collections::VecDeque;
 
 /// The minimum stack size for a thread in the styling pool, in kilobytes.
diff --git a/servo/components/style/parser.rs b/servo/components/style/parser.rs
index 893625854f..1e339841a9 100644
--- a/servo/components/style/parser.rs
+++ b/servo/components/style/parser.rs
@@ -9,9 +9,64 @@ use crate::error_reporting::{ContextualParseError, ParseErrorReporter};
 use crate::stylesheets::{CssRuleType, CssRuleTypes, Namespaces, Origin, UrlExtraData};
 use crate::use_counters::UseCounters;
 use cssparser::{Parser, SourceLocation, UnicodeRange};
+use selectors::parser::ParseRelative;
 use std::borrow::Cow;
 use style_traits::{OneOrMoreSeparated, ParseError, ParsingMode, Separator};
 
+/// Nesting context for parsing rules.
+#[derive(Clone, Copy)]
+pub struct NestingContext {
+    /// All rule types we've nested into, if any.
+    pub rule_types: CssRuleTypes,
+    /// Whether or not parsing relative selector syntax should be allowed.
+    pub parse_relative: ParseRelative,
+}
+
+impl NestingContext {
+    fn parse_relative_for(rule_type: CssRuleType) -> ParseRelative {
+        match rule_type {
+            CssRuleType::Scope => ParseRelative::ForScope,
+            CssRuleType::Style => ParseRelative::ForNesting,
+            _ => ParseRelative::No,
+        }
+    }
+
+    /// Create a new nesting context.
+    pub fn new(rule_types: CssRuleTypes, parse_nested_rule_type: Option<CssRuleType>) -> Self {
+        Self {
+            rule_types,
+            parse_relative: parse_nested_rule_type
+                .map_or(ParseRelative::No, Self::parse_relative_for)
+        }
+    }
+
+    /// Create a new nesting context based on the given rule.
+    pub fn new_from_rule(rule_type: Option<CssRuleType>) -> Self {
+        Self {
+            rule_types: rule_type.map(CssRuleTypes::from).unwrap_or_default(),
+            parse_relative: rule_type
+                .map(Self::parse_relative_for)
+                .unwrap_or(ParseRelative::No),
+        }
+    }
+
+    /// Save the current nesting context.
+    pub fn save(&mut self, rule_type: CssRuleType) -> Self {
+        let old = *self;
+        self.rule_types.insert(rule_type);
+        let new_parse_relative = Self::parse_relative_for(rule_type);
+        if new_parse_relative != ParseRelative::No {
+            self.parse_relative = new_parse_relative;
+        }
+        old
+    }
+
+    /// Load the saved nesting context.
+    pub fn restore(&mut self, saved: Self) {
+        *self = saved;
+    }
+}
+
 /// The data that the parser needs from outside in order to parse a stylesheet.
 pub struct ParserContext<'a> {
     /// The `Origin` of the stylesheet, whether it's a user, author or
@@ -19,8 +74,6 @@ pub struct ParserContext<'a> {
     pub stylesheet_origin: Origin,
     /// The extra data we need for resolving url values.
     pub url_data: &'a UrlExtraData,
-    /// The current rule types, if any.
-    pub rule_types: CssRuleTypes,
     /// The mode to use when parsing.
     pub parsing_mode: ParsingMode,
     /// The quirks mode of this stylesheet.
@@ -31,6 +84,8 @@ pub struct ParserContext<'a> {
     pub namespaces: Cow<'a, Namespaces>,
     /// The use counters we want to record while parsing style rules, if any.
     pub use_counters: Option<&'a UseCounters>,
+    /// Current nesting context.
+    pub nesting_context: NestingContext,
 }
 
 impl<'a> ParserContext<'a> {
@@ -49,12 +104,12 @@ impl<'a> ParserContext<'a> {
         Self {
             stylesheet_origin,
             url_data,
-            rule_types: rule_type.map(CssRuleTypes::from).unwrap_or_default(),
             parsing_mode,
             quirks_mode,
             error_reporter,
             namespaces,
             use_counters,
+            nesting_context: NestingContext::new_from_rule(rule_type),
         }
     }
 
@@ -64,22 +119,21 @@ impl<'a> ParserContext<'a> {
         rule_type: CssRuleType,
         cb: impl FnOnce(&mut Self) -> R,
     ) -> R {
-        let old_rule_types = self.rule_types;
-        self.rule_types.insert(rule_type);
+        let old = self.nesting_context.save(rule_type);
         let r = cb(self);
-        self.rule_types = old_rule_types;
+        self.nesting_context.restore(old);
         r
     }
 
     /// Whether we're in a @page rule.
     #[inline]
     pub fn in_page_rule(&self) -> bool {
-        self.rule_types.contains(CssRuleType::Page)
+        self.nesting_context.rule_types.contains(CssRuleType::Page)
     }
 
     /// Get the rule type, which assumes that one is available.
     pub fn rule_types(&self) -> CssRuleTypes {
-        self.rule_types
+        self.nesting_context.rule_types
     }
 
     /// Returns whether CSS error reporting is enabled.
diff --git a/servo/components/style/properties/build.py b/servo/components/style/properties/build.py
index 42121a4eae..d1f76d4a25 100644
--- a/servo/components/style/properties/build.py
+++ b/servo/components/style/properties/build.py
@@ -20,36 +20,10 @@ RE_PYTHON_ADDR = re.compile(r"<.+? object at 0x[0-9a-fA-F]+>")
 
 OUT_DIR = os.environ.get("OUT_DIR", "")
 
-STYLE_STRUCT_LIST = [
-    "background",
-    "border",
-    "box",
-    "column",
-    "counters",
-    "effects",
-    "font",
-    "inherited_box",
-    "inherited_svg",
-    "inherited_table",
-    "inherited_text",
-    "inherited_ui",
-    "list",
-    "margin",
-    "outline",
-    "page",
-    "padding",
-    "position",
-    "svg",
-    "table",
-    "text",
-    "ui",
-    "xul",
-]
-
 
 def main():
     usage = (
-        "Usage: %s [ servo-2013 | servo-2020 | gecko ] [ style-crate | geckolib <template> | html ]"
+        "Usage: %s [ servo | gecko ] [ style-crate | geckolib <template> ]"
         % sys.argv[0]
     )
     if len(sys.argv) < 3:
@@ -57,29 +31,15 @@ def main():
     engine = sys.argv[1]
     output = sys.argv[2]
 
-    if engine not in ["servo-2013", "servo-2020", "gecko"] or output not in [
+    if engine not in ["servo", "gecko"] or output not in [
         "style-crate",
         "geckolib",
-        "html",
     ]:
         abort(usage)
 
     properties = data.PropertiesData(engine=engine)
-    files = {}
-    for kind in ["longhands", "shorthands"]:
-        files[kind] = {}
-        for struct in STYLE_STRUCT_LIST:
-            file_name = os.path.join(BASE, kind, "{}.mako.rs".format(struct))
-            if kind == "shorthands" and not os.path.exists(file_name):
-                files[kind][struct] = ""
-                continue
-            files[kind][struct] = render(
-                file_name,
-                engine=engine,
-                data=properties,
-            )
     properties_template = os.path.join(BASE, "properties.mako.rs")
-    files["properties"] = render(
+    properties_file = render(
         properties_template,
         engine=engine,
         data=properties,
@@ -87,31 +47,15 @@ def main():
         OUT_DIR=OUT_DIR,
     )
     if output == "style-crate":
-        write(OUT_DIR, "properties.rs", files["properties"])
-        for kind in ["longhands", "shorthands"]:
-            for struct in files[kind]:
-                write(
-                    os.path.join(OUT_DIR, kind),
-                    "{}.rs".format(struct),
-                    files[kind][struct],
-                )
-
-        if engine == "gecko":
-            template = os.path.join(BASE, "gecko.mako.rs")
-            rust = render(template, data=properties)
-            write(OUT_DIR, "gecko_properties.rs", rust)
-
-        if engine in ["servo-2013", "servo-2020"]:
-            if engine == "servo-2013":
-                pref_attr = "servo_2013_pref"
-            if engine == "servo-2020":
-                pref_attr = "servo_2020_pref"
+        write(OUT_DIR, "properties.rs", properties_file)
+
+        if engine == "servo":
             properties_dict = {
                 kind: {
-                    p.name: {"pref": getattr(p, pref_attr)}
+                    p.name: {"pref": getattr(p, "servo_pref")}
                     for prop in properties_list
                     if prop.enabled_in_content()
-                    for p in [prop] + prop.alias
+                    for p in [prop] + prop.aliases
                 }
                 for kind, properties_list in [
                     ("longhands", properties.longhands),
diff --git a/servo/components/style/properties/cascade.rs b/servo/components/style/properties/cascade.rs
index d4d48eaeb8..0f264a9249 100644
--- a/servo/components/style/properties/cascade.rs
+++ b/servo/components/style/properties/cascade.rs
@@ -297,7 +297,7 @@ where
     context.style().add_flags(cascade_input_flags);
 
     let using_cached_reset_properties;
-    let ignore_colors = !context.builder.device.use_document_colors();
+    let ignore_colors = context.builder.device.forced_colors().is_active();
     let mut cascade = Cascade::new(first_line_reparenting, ignore_colors);
     let mut declarations = Default::default();
     let mut shorthand_cache = ShorthandsWithPropertyReferencesCache::default();
@@ -763,6 +763,11 @@ impl<'b> Cascade<'b> {
 
         if apply!(Zoom) {
             self.compute_zoom(context);
+            // NOTE(emilio): This is a bit of a hack, but matches the shipped WebKit and Blink
+            // behavior for now. Ideally, in the future, we have a pass over all
+            // implicitly-or-explicitly-inherited properties that can contain lengths and
+            // re-compute them properly, see https://github.com/w3c/csswg-drafts/issues/9397.
+            self.recompute_font_size_for_zoom_change(&mut context.builder);
         }
 
         // Compute font-family.
@@ -1226,8 +1231,6 @@ impl<'b> Cascade<'b> {
     /// <svg:text> is not affected by text zoom, and it uses a preshint to disable it. We fix up
     /// the struct when this happens by unzooming its contained font values, which will have been
     /// zoomed in the parent.
-    ///
-    /// FIXME(emilio): Why doing this _before_ handling font-size? That sounds wrong.
     #[cfg(feature = "gecko")]
     fn unzoom_fonts_if_needed(&self, builder: &mut StyleBuilder) {
         debug_assert!(self.seen.contains(LonghandId::XTextScale));
@@ -1250,6 +1253,19 @@ impl<'b> Cascade<'b> {
         builder.mutate_font().unzoom_fonts(device);
     }
 
+    fn recompute_font_size_for_zoom_change(&self, builder: &mut StyleBuilder) {
+        debug_assert!(self.seen.contains(LonghandId::Zoom));
+        // NOTE(emilio): Intentionally not using the effective zoom here, since all the inherited
+        // zooms are already applied.
+        let zoom = builder.get_box().clone_zoom();
+        let old_size = builder.get_font().clone_font_size();
+        let new_size = old_size.zoom(zoom);
+        if old_size == new_size {
+            return;
+        }
+        builder.mutate_font().set_font_size(new_size);
+    }
+
     /// Special handling of font-size: math (used for MathML).
     /// https://w3c.github.io/mathml-core/#the-math-script-level-property
     /// TODO: Bug: 1548471: MathML Core also does not specify a script min size
diff --git a/servo/components/style/properties/data.py b/servo/components/style/properties/data.py
index 093f1cb75f..2a29a7ed58 100644
--- a/servo/components/style/properties/data.py
+++ b/servo/components/style/properties/data.py
@@ -176,11 +176,9 @@ class Keyword(object):
         gecko_enum_prefix=None,
         custom_consts=None,
         extra_gecko_values=None,
-        extra_servo_2013_values=None,
-        extra_servo_2020_values=None,
+        extra_servo_values=None,
         gecko_aliases=None,
-        servo_2013_aliases=None,
-        servo_2020_aliases=None,
+        servo_aliases=None,
         gecko_strip_moz_prefix=None,
         gecko_inexhaustive=None,
     ):
@@ -196,11 +194,9 @@ class Keyword(object):
         )
         self.gecko_enum_prefix = gecko_enum_prefix
         self.extra_gecko_values = (extra_gecko_values or "").split()
-        self.extra_servo_2013_values = (extra_servo_2013_values or "").split()
-        self.extra_servo_2020_values = (extra_servo_2020_values or "").split()
+        self.extra_servo_values = (extra_servo_values or "").split()
         self.gecko_aliases = parse_aliases(gecko_aliases or "")
-        self.servo_2013_aliases = parse_aliases(servo_2013_aliases or "")
-        self.servo_2020_aliases = parse_aliases(servo_2020_aliases or "")
+        self.servo_aliases = parse_aliases(servo_aliases or "")
         self.consts_map = {} if custom_consts is None else custom_consts
         self.gecko_strip_moz_prefix = (
             True if gecko_strip_moz_prefix is None else gecko_strip_moz_prefix
@@ -210,20 +206,16 @@ class Keyword(object):
     def values_for(self, engine):
         if engine == "gecko":
             return self.values + self.extra_gecko_values
-        elif engine == "servo-2013":
-            return self.values + self.extra_servo_2013_values
-        elif engine == "servo-2020":
-            return self.values + self.extra_servo_2020_values
+        elif engine == "servo":
+            return self.values + self.extra_servo_values
         else:
             raise Exception("Bad engine: " + engine)
 
     def aliases_for(self, engine):
         if engine == "gecko":
             return self.gecko_aliases
-        elif engine == "servo-2013":
-            return self.servo_2013_aliases
-        elif engine == "servo-2020":
-            return self.servo_2020_aliases
+        elif engine == "servo":
+            return self.servo_aliases
         else:
             raise Exception("Bad engine: " + engine)
 
@@ -289,8 +281,7 @@ class Property(object):
         self,
         name,
         spec,
-        servo_2013_pref,
-        servo_2020_pref,
+        servo_pref,
         gecko_pref,
         enabled_in,
         rule_types_allowed,
@@ -304,8 +295,7 @@ class Property(object):
         self.spec = spec
         self.ident = to_rust_ident(name)
         self.camel_case = to_camel_case(self.ident)
-        self.servo_2013_pref = servo_2013_pref
-        self.servo_2020_pref = servo_2020_pref
+        self.servo_pref = servo_pref
         self.gecko_pref = gecko_pref
         self.rule_types_allowed = rule_values_from_arg(rule_types_allowed)
         # For enabled_in, the setup is as follows:
@@ -329,10 +319,8 @@ class Property(object):
     def experimental(self, engine):
         if engine == "gecko":
             return bool(self.gecko_pref)
-        elif engine == "servo-2013":
-            return bool(self.servo_2013_pref)
-        elif engine == "servo-2020":
-            return bool(self.servo_2020_pref)
+        elif engine == "servo":
+            return bool(self.servo_pref)
         else:
             raise Exception("Bad engine: " + engine)
 
@@ -364,8 +352,7 @@ class Longhand(Property):
         animation_value_type=None,
         keyword=None,
         predefined_type=None,
-        servo_2013_pref=None,
-        servo_2020_pref=None,
+        servo_pref=None,
         gecko_pref=None,
         enabled_in="content",
         need_index=False,
@@ -390,8 +377,7 @@ class Longhand(Property):
             self,
             name=name,
             spec=spec,
-            servo_2013_pref=servo_2013_pref,
-            servo_2020_pref=servo_2020_pref,
+            servo_pref=servo_pref,
             gecko_pref=gecko_pref,
             enabled_in=enabled_in,
             rule_types_allowed=rule_types_allowed,
@@ -518,16 +504,8 @@ class Longhand(Property):
     def may_be_disabled_in(self, shorthand, engine):
         if engine == "gecko":
             return self.gecko_pref and self.gecko_pref != shorthand.gecko_pref
-        elif engine == "servo-2013":
-            return (
-                self.servo_2013_pref
-                and self.servo_2013_pref != shorthand.servo_2013_pref
-            )
-        elif engine == "servo-2020":
-            return (
-                self.servo_2020_pref
-                and self.servo_2020_pref != shorthand.servo_2020_pref
-            )
+        elif engine == "servo":
+            return self.servo_pref and self.servo_pref != shorthand.servo_pref
         else:
             raise Exception("Bad engine: " + engine)
 
@@ -659,8 +637,7 @@ class Shorthand(Property):
         name,
         sub_properties,
         spec=None,
-        servo_2013_pref=None,
-        servo_2020_pref=None,
+        servo_pref=None,
         gecko_pref=None,
         enabled_in="content",
         rule_types_allowed=DEFAULT_RULES,
@@ -672,8 +649,7 @@ class Shorthand(Property):
             self,
             name=name,
             spec=spec,
-            servo_2013_pref=servo_2013_pref,
-            servo_2020_pref=servo_2020_pref,
+            servo_pref=servo_pref,
             gecko_pref=gecko_pref,
             enabled_in=enabled_in,
             rule_types_allowed=rule_types_allowed,
@@ -704,8 +680,7 @@ class Alias(object):
         self.original = original
         self.enabled_in = original.enabled_in
         self.animatable = original.animatable
-        self.servo_2013_pref = original.servo_2013_pref
-        self.servo_2020_pref = original.servo_2020_pref
+        self.servo_pref = original.servo_pref
         self.gecko_pref = gecko_pref
         self.rule_types_allowed = original.rule_types_allowed
         self.flags = original.flags
@@ -722,10 +697,8 @@ class Alias(object):
     def experimental(self, engine):
         if engine == "gecko":
             return bool(self.gecko_pref)
-        elif engine == "servo-2013":
-            return bool(self.servo_2013_pref)
-        elif engine == "servo-2020":
-            return bool(self.servo_2020_pref)
+        elif engine == "servo":
+            return bool(self.servo_pref)
         else:
             raise Exception("Bad engine: " + engine)
 
@@ -768,7 +741,7 @@ class Method(object):
 
 
 class StyleStruct(object):
-    def __init__(self, name, inherited, gecko_name=None, additional_methods=None):
+    def __init__(self, name, inherited, gecko_name=None):
         self.gecko_struct_name = "Gecko" + name
         self.name = name
         self.name_lower = to_snake_case(name)
@@ -777,15 +750,12 @@ class StyleStruct(object):
         self.inherited = inherited
         self.gecko_name = gecko_name or name
         self.gecko_ffi_name = "nsStyle" + self.gecko_name
-        self.additional_methods = additional_methods or []
         self.document_dependent = self.gecko_name in ["Font", "Visibility", "Text"]
 
 
 class PropertiesData(object):
     def __init__(self, engine):
         self.engine = engine
-        self.style_structs = []
-        self.current_style_struct = None
         self.longhands = []
         self.longhands_by_name = {}
         self.longhands_by_logical_group = {}
@@ -797,13 +767,35 @@ class PropertiesData(object):
             CountedUnknownProperty(p) for p in COUNTED_UNKNOWN_PROPERTIES
         ]
 
-    def new_style_struct(self, *args, **kwargs):
-        style_struct = StyleStruct(*args, **kwargs)
-        self.style_structs.append(style_struct)
-        self.current_style_struct = style_struct
+        self.style_structs = [
+            StyleStruct("Background", inherited=False),
+            StyleStruct("Border", inherited=False),
+            StyleStruct("Box", inherited=False, gecko_name="Display"),
+            StyleStruct("Column", inherited=False),
+            StyleStruct("Counters", inherited=False, gecko_name="Content"),
+            StyleStruct("Effects", inherited=False),
+            StyleStruct("Font", inherited=True),
+            StyleStruct("InheritedBox", inherited=True, gecko_name="Visibility"),
+            StyleStruct("InheritedSVG", inherited=True, gecko_name="SVG"),
+            StyleStruct("InheritedTable", inherited=True, gecko_name="TableBorder"),
+            StyleStruct("InheritedText", inherited=True, gecko_name="Text"),
+            StyleStruct("InheritedUI", inherited=True, gecko_name="UI"),
+            StyleStruct("List", inherited=True),
+            StyleStruct("Margin", inherited=False),
+            StyleStruct("Outline", inherited=False),
+            StyleStruct("Padding", inherited=False),
+            StyleStruct("Page", inherited=False),
+            StyleStruct("Position", inherited=False),
+            StyleStruct("SVG", inherited=False, gecko_name="SVGReset"),
+            StyleStruct("Table", inherited=False),
+            StyleStruct("Text", inherited=False, gecko_name="TextReset"),
+            StyleStruct("UI", inherited=False, gecko_name="UIReset"),
+            StyleStruct("XUL", inherited=False),
+        ]
+        self.current_style_struct = None
 
     def active_style_structs(self):
-        return [s for s in self.style_structs if s.additional_methods or s.longhands]
+        return [s for s in self.style_structs if s.longhands]
 
     def add_prefixed_aliases(self, property):
         # FIXME Servo's DOM architecture doesn't support vendor-prefixed properties.
@@ -856,7 +848,7 @@ def _add_logical_props(data, props):
     groups = set()
     for prop in props:
         if prop not in data.longhands_by_name:
-            assert data.engine in ["servo-2013", "servo-2020"]
+            assert data.engine == "servo"
             continue
         prop = data.longhands_by_name[prop]
         if prop.logical_group:
diff --git a/servo/components/style/properties/declaration_block.rs b/servo/components/style/properties/declaration_block.rs
index 81d7148e62..94945ab8c0 100644
--- a/servo/components/style/properties/declaration_block.rs
+++ b/servo/components/style/properties/declaration_block.rs
@@ -36,10 +36,10 @@ use cssparser::{
 use itertools::Itertools;
 use selectors::SelectorList;
 use servo_arc::Arc;
-use smallbitvec::{self, SmallBitVec};
+use smallbitvec::SmallBitVec;
 use smallvec::SmallVec;
 use std::fmt::{self, Write};
-use std::iter::{DoubleEndedIterator, Zip};
+use std::iter::Zip;
 use std::slice::Iter;
 use style_traits::{CssWriter, ParseError, ParsingMode, StyleParseErrorKind, ToCss};
 use thin_vec::ThinVec;
diff --git a/servo/components/style/properties/helpers.mako.rs b/servo/components/style/properties/helpers.mako.rs
index 968a97aa00..82998632ca 100644
--- a/servo/components/style/properties/helpers.mako.rs
+++ b/servo/components/style/properties/helpers.mako.rs
@@ -594,11 +594,9 @@
             'gecko_constant_prefix',
             'gecko_enum_prefix',
             'extra_gecko_values',
-            'extra_servo_2013_values',
-            'extra_servo_2020_values',
+            'extra_servo_values',
             'gecko_aliases',
-            'servo_2013_aliases',
-            'servo_2020_aliases',
+            'servo_aliases',
             'custom_consts',
             'gecko_inexhaustive',
             'gecko_strip_moz_prefix',
diff --git a/servo/components/style/properties/helpers/animated_properties.mako.rs b/servo/components/style/properties/helpers/animated_properties.mako.rs
index 290684cdab..171413b243 100644
--- a/servo/components/style/properties/helpers/animated_properties.mako.rs
+++ b/servo/components/style/properties/helpers/animated_properties.mako.rs
@@ -737,7 +737,7 @@ impl<'a> TransitionPropertyIterator<'a> {
 /// A single iteration of the TransitionPropertyIterator.
 pub struct TransitionPropertyIteration {
     /// The id of the longhand for this property.
-    pub longhand_id: LonghandId,
+    pub property: OwnedPropertyDeclarationId,
 
     /// The index of this property in the list of transition properties for this
     /// iterator's style.
@@ -753,7 +753,7 @@ impl<'a> Iterator for TransitionPropertyIterator<'a> {
             if let Some(ref mut longhand_iterator) = self.longhand_iterator {
                 if let Some(longhand_id) = longhand_iterator.next() {
                     return Some(TransitionPropertyIteration {
-                        longhand_id,
+                        property: OwnedPropertyDeclarationId::Longhand(longhand_id),
                         index: self.index_range.start - 1,
                     });
                 }
@@ -766,7 +766,7 @@ impl<'a> Iterator for TransitionPropertyIterator<'a> {
                     match id.longhand_or_shorthand() {
                         Ok(longhand_id) => {
                             return Some(TransitionPropertyIteration {
-                                longhand_id,
+                                property: OwnedPropertyDeclarationId::Longhand(longhand_id),
                                 index,
                             });
                         },
@@ -778,7 +778,13 @@ impl<'a> Iterator for TransitionPropertyIterator<'a> {
                         },
                     }
                 }
-                TransitionProperty::Custom(..) | TransitionProperty::Unsupported(..) => {}
+                TransitionProperty::Custom(name) => {
+                    return Some(TransitionPropertyIteration {
+                        property: OwnedPropertyDeclarationId::Custom(name),
+                        index,
+                    })
+                },
+                TransitionProperty::Unsupported(..) => {},
             }
         }
     }
diff --git a/servo/components/style/properties/longhands/background.mako.rs b/servo/components/style/properties/longhands/background.mako.rs
index 48270f748e..535dd64e20 100644
--- a/servo/components/style/properties/longhands/background.mako.rs
+++ b/servo/components/style/properties/longhands/background.mako.rs
@@ -4,13 +4,11 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<% data.new_style_struct("Background", inherited=False) %>
-
 ${helpers.predefined_type(
     "background-color",
     "Color",
     "computed::Color::TRANSPARENT_BLACK",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="SpecifiedValue::transparent()",
     spec="https://drafts.csswg.org/css-backgrounds/#background-color",
     animation_value_type="AnimatedColor",
@@ -23,7 +21,7 @@ ${helpers.predefined_type(
 ${helpers.predefined_type(
     "background-image",
     "Image",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_value="computed::Image::None",
     initial_specified_value="specified::Image::None",
     spec="https://drafts.csswg.org/css-backgrounds/#the-background-image",
@@ -38,7 +36,7 @@ ${helpers.predefined_type(
         "background-position-" + axis,
         "position::" + direction + "Position",
         "computed::LengthPercentage::zero_percent()",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         initial_specified_value="SpecifiedValue::initial_specified_value()",
         spec="https://drafts.csswg.org/css-backgrounds-4/#propdef-background-position-" + axis,
         animation_value_type="ComputedValue",
@@ -52,7 +50,7 @@ ${helpers.predefined_type(
     "background-repeat",
     "BackgroundRepeat",
     "computed::BackgroundRepeat::repeat()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::BackgroundRepeat::repeat()",
     animation_value_type="discrete",
     vector=True,
@@ -62,8 +60,8 @@ ${helpers.predefined_type(
 
 ${helpers.single_keyword(
     "background-attachment",
-    "scroll" + (" fixed" if engine in ["gecko", "servo-2013"] else "") + (" local" if engine == "gecko" else ""),
-    engines="gecko servo-2013 servo-2020",
+    "scroll fixed" + (" local" if engine == "gecko" else ""),
+    engines="gecko servo",
     vector=True,
     gecko_enum_prefix="StyleImageLayerAttachment",
     spec="https://drafts.csswg.org/css-backgrounds/#the-background-attachment",
@@ -74,7 +72,7 @@ ${helpers.single_keyword(
 ${helpers.single_keyword(
     "background-clip",
     "border-box padding-box content-box",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     extra_gecko_values="text",
     vector=True, extra_prefixes="webkit",
     gecko_enum_prefix="StyleGeometryBox",
@@ -87,7 +85,7 @@ ${helpers.single_keyword(
 ${helpers.single_keyword(
     "background-origin",
     "padding-box border-box content-box",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     vector=True, extra_prefixes="webkit",
     gecko_enum_prefix="StyleGeometryBox",
     gecko_inexhaustive=True,
@@ -99,7 +97,7 @@ ${helpers.single_keyword(
 ${helpers.predefined_type(
     "background-size",
     "BackgroundSize",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_value="computed::BackgroundSize::auto()",
     initial_specified_value="specified::BackgroundSize::auto()",
     spec="https://drafts.csswg.org/css-backgrounds/#the-background-size",
diff --git a/servo/components/style/properties/longhands/border.mako.rs b/servo/components/style/properties/longhands/border.mako.rs
index 4d0676f678..59a0fee94a 100644
--- a/servo/components/style/properties/longhands/border.mako.rs
+++ b/servo/components/style/properties/longhands/border.mako.rs
@@ -3,11 +3,8 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
-<% from data import Keyword, Method, ALL_CORNERS, PHYSICAL_SIDES, ALL_SIDES, maybe_moz_logical_alias %>
+<% from data import ALL_CORNERS, ALL_SIDES, maybe_moz_logical_alias %>
 
-<% data.new_style_struct("Border", inherited=False,
-                   additional_methods=[Method("border_" + side + "_has_nonzero_width",
-                                              "bool") for side in ["top", "right", "bottom", "left"]]) %>
 <%
     def maybe_logical_spec(side, kind):
         if side[1]: # if it is logical
@@ -23,7 +20,7 @@
     ${helpers.predefined_type(
         "border-%s-color" % side_name, "Color",
         "computed_value::T::currentcolor()",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         aliases=maybe_moz_logical_alias(engine, side, "-moz-border-%s-color"),
         spec=maybe_logical_spec(side, "color"),
         animation_value_type="AnimatedColor",
@@ -37,7 +34,7 @@
     ${helpers.predefined_type(
         "border-%s-style" % side_name, "BorderStyle",
         "specified::BorderStyle::None",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         aliases=maybe_moz_logical_alias(engine, side, "-moz-border-%s-style"),
         spec=maybe_logical_spec(side, "style"),
         animation_value_type="discrete" if not is_logical else "none",
@@ -50,7 +47,7 @@
         "border-%s-width" % side_name,
         "BorderSideWidth",
         "app_units::Au::from_px(3)",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         aliases=maybe_moz_logical_alias(engine, side, "-moz-border-%s-width"),
         spec=maybe_logical_spec(side, "width"),
         animation_value_type="NonNegativeLength",
@@ -76,7 +73,7 @@
         "BorderCornerRadius",
         "computed::BorderCornerRadius::zero()",
         "parse",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         extra_prefixes=prefixes,
         spec=maybe_logical_spec(corner, "radius"),
         boxed=True,
@@ -111,13 +108,13 @@ ${helpers.single_keyword(
 ${helpers.predefined_type(
     "border-image-source",
     "Image",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_value="computed::Image::None",
     initial_specified_value="specified::Image::None",
     spec="https://drafts.csswg.org/css-backgrounds/#the-background-image",
     vector=False,
     animation_value_type="discrete",
-    boxed=engine == "servo-2013",
+    boxed=engine == "servo",
     ignored_when_colors_disabled=True,
     affects="paint",
 )}
@@ -125,7 +122,7 @@ ${helpers.predefined_type(
 ${helpers.predefined_type(
     "border-image-outset",
     "NonNegativeLengthOrNumberRect",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_value="generics::rect::Rect::all(computed::NonNegativeLengthOrNumber::zero())",
     initial_specified_value="generics::rect::Rect::all(specified::NonNegativeLengthOrNumber::zero())",
     spec="https://drafts.csswg.org/css-backgrounds/#border-image-outset",
@@ -138,7 +135,7 @@ ${helpers.predefined_type(
     "border-image-repeat",
     "BorderImageRepeat",
     "computed::BorderImageRepeat::stretch()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::BorderImageRepeat::stretch()",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-backgrounds/#the-border-image-repeat",
@@ -148,7 +145,7 @@ ${helpers.predefined_type(
 ${helpers.predefined_type(
     "border-image-width",
     "BorderImageWidth",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_value="computed::BorderImageWidth::all(computed::BorderImageSideWidth::one())",
     initial_specified_value="specified::BorderImageWidth::all(specified::BorderImageSideWidth::one())",
     spec="https://drafts.csswg.org/css-backgrounds/#border-image-width",
@@ -160,7 +157,7 @@ ${helpers.predefined_type(
 ${helpers.predefined_type(
     "border-image-slice",
     "BorderImageSlice",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_value="computed::BorderImageSlice::hundred_percent()",
     initial_specified_value="specified::BorderImageSlice::hundred_percent()",
     spec="https://drafts.csswg.org/css-backgrounds/#border-image-slice",
diff --git a/servo/components/style/properties/longhands/box.mako.rs b/servo/components/style/properties/longhands/box.mako.rs
index 017bef38ea..187e8f8169 100644
--- a/servo/components/style/properties/longhands/box.mako.rs
+++ b/servo/components/style/properties/longhands/box.mako.rs
@@ -3,17 +3,13 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
-<% from data import ALL_AXES, Keyword, Method, to_rust_ident, to_camel_case%>
-
-<% data.new_style_struct("Box",
-                         inherited=False,
-                         gecko_name="Display") %>
+<% from data import ALL_AXES %>
 
 ${helpers.predefined_type(
     "display",
     "Display",
     "computed::Display::inline()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::Display::inline()",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-display/#propdef-display",
@@ -38,7 +34,7 @@ ${helpers.single_keyword(
 ${helpers.single_keyword(
     "-servo-top-layer",
     "none top",
-    engines="servo-2013 servo-2020",
+    engines="servo",
     animation_value_type="none",
     enabled_in="ua",
     spec="Internal (not web-exposed)",
@@ -47,8 +43,8 @@ ${helpers.single_keyword(
 
 <%helpers:single_keyword
     name="position"
-    values="static absolute relative fixed ${'sticky' if engine in ['gecko', 'servo-2013'] else ''}"
-    engines="gecko servo-2013 servo-2020"
+    values="static absolute relative fixed sticky"
+    engines="gecko servo"
     animation_value_type="discrete"
     gecko_enum_prefix="StylePositionProperty"
     spec="https://drafts.csswg.org/css-position/#position-property"
@@ -69,8 +65,7 @@ ${helpers.predefined_type(
     "float",
     "Float",
     "computed::Float::None",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
     initial_specified_value="specified::Float::None",
     spec="https://drafts.csswg.org/css-box/#propdef-float",
     animation_value_type="discrete",
@@ -83,7 +78,7 @@ ${helpers.predefined_type(
     "clear",
     "Clear",
     "computed::Clear::None",
-    engines="gecko servo-2013",
+    engines="gecko servo",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css2/#propdef-clear",
     servo_restyle_damage="rebuild_and_reflow",
@@ -94,7 +89,7 @@ ${helpers.predefined_type(
     "vertical-align",
     "VerticalAlign",
     "computed::VerticalAlign::baseline()",
-    engines="gecko servo-2013",
+    engines="gecko servo",
     animation_value_type="ComputedValue",
     spec="https://www.w3.org/TR/CSS2/visudet.html#propdef-vertical-align",
     servo_restyle_damage = "reflow",
@@ -105,7 +100,7 @@ ${helpers.predefined_type(
     "baseline-source",
     "BaselineSource",
     "computed::BaselineSource::Auto",
-    engines="gecko servo-2013",
+    engines="gecko servo",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-inline-3/#baseline-source",
     servo_restyle_damage = "reflow",
@@ -117,7 +112,8 @@ ${helpers.predefined_type(
 ${helpers.single_keyword(
     "-servo-overflow-clip-box",
     "padding-box content-box",
-    engines="servo-2013",
+    engines="servo",
+    servo_pref="layout.legacy_layout",
     animation_value_type="none",
     enabled_in="ua",
     spec="Internal, not web-exposed, \
@@ -146,7 +142,7 @@ ${helpers.single_keyword(
         full_name,
         "Overflow",
         "computed::Overflow::Visible",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         logical_group="overflow",
         logical=logical,
         animation_value_type="discrete",
@@ -174,7 +170,7 @@ ${helpers.predefined_type(
     "transform",
     "Transform",
     "generics::transform::Transform::none()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     extra_prefixes=transform_extra_prefixes,
     animation_value_type="ComputedValue",
     flags="CAN_ANIMATE_ON_COMPOSITOR",
@@ -187,7 +183,7 @@ ${helpers.predefined_type(
     "rotate",
     "Rotate",
     "generics::transform::Rotate::None",
-    engines="gecko servo-2013",
+    engines="gecko servo",
     animation_value_type="ComputedValue",
     boxed=True,
     flags="CAN_ANIMATE_ON_COMPOSITOR",
@@ -201,7 +197,7 @@ ${helpers.predefined_type(
     "scale",
     "Scale",
     "generics::transform::Scale::None",
-    engines="gecko servo-2013",
+    engines="gecko servo",
     animation_value_type="ComputedValue",
     boxed=True,
     flags="CAN_ANIMATE_ON_COMPOSITOR",
@@ -215,7 +211,7 @@ ${helpers.predefined_type(
     "translate",
     "Translate",
     "generics::transform::Translate::None",
-    engines="gecko servo-2013",
+    engines="gecko servo",
     animation_value_type="ComputedValue",
     boxed=True,
     flags="CAN_ANIMATE_ON_COMPOSITOR",
@@ -285,7 +281,6 @@ ${helpers.predefined_type(
     "computed::OffsetPosition::normal()",
     engines="gecko",
     animation_value_type="ComputedValue",
-    gecko_pref="layout.css.motion-path-offset-position.enabled",
     flags="CAN_ANIMATE_ON_COMPOSITOR",
     spec="https://drafts.fxtf.org/motion-1/#offset-position-property",
     servo_restyle_damage="reflow_out_of_flow",
@@ -409,7 +404,7 @@ ${helpers.predefined_type(
     "perspective",
     "Perspective",
     "computed::Perspective::none()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     gecko_ffi_name="mChildPerspective",
     spec="https://drafts.csswg.org/css-transforms/#perspective",
     extra_prefixes=transform_extra_prefixes,
@@ -422,7 +417,7 @@ ${helpers.predefined_type(
     "perspective-origin",
     "Position",
     "computed::position::Position::center()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     boxed=True,
     extra_prefixes=transform_extra_prefixes,
     spec="https://drafts.csswg.org/css-transforms-2/#perspective-origin-property",
@@ -434,7 +429,7 @@ ${helpers.predefined_type(
 ${helpers.single_keyword(
     "backface-visibility",
     "visible hidden",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     gecko_enum_prefix="StyleBackfaceVisibility",
     spec="https://drafts.csswg.org/css-transforms/#backface-visibility-property",
     extra_prefixes=transform_extra_prefixes,
@@ -456,7 +451,7 @@ ${helpers.predefined_type(
     "transform-style",
     "TransformStyle",
     "computed::TransformStyle::Flat",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-transforms-2/#transform-style-property",
     extra_prefixes=transform_extra_prefixes,
     animation_value_type="discrete",
@@ -468,7 +463,7 @@ ${helpers.predefined_type(
     "transform-origin",
     "TransformOrigin",
     "computed::TransformOrigin::initial_value()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     animation_value_type="ComputedValue",
     extra_prefixes=transform_extra_prefixes,
     gecko_ffi_name="mTransformOrigin",
@@ -503,10 +498,11 @@ ${helpers.predefined_type(
     "container-type",
     "ContainerType",
     "computed::ContainerType::Normal",
-    engines="gecko",
+    engines="gecko servo",
     animation_value_type="none",
     enabled_in="ua",
     gecko_pref="layout.css.container-queries.enabled",
+    servo_pref="layout.container-queries.enabled",
     spec="https://drafts.csswg.org/css-contain-3/#container-type",
     affects="layout",
 )}
@@ -515,10 +511,11 @@ ${helpers.predefined_type(
     "container-name",
     "ContainerName",
     "computed::ContainerName::none()",
-    engines="gecko",
+    engines="gecko servo",
     animation_value_type="none",
     enabled_in="ua",
     gecko_pref="layout.css.container-queries.enabled",
+    servo_pref="layout.container-queries.enabled",
     spec="https://drafts.csswg.org/css-contain-3/#container-name",
     affects="",
 )}
diff --git a/servo/components/style/properties/longhands/column.mako.rs b/servo/components/style/properties/longhands/column.mako.rs
index 38c32938c6..ca97f36dba 100644
--- a/servo/components/style/properties/longhands/column.mako.rs
+++ b/servo/components/style/properties/longhands/column.mako.rs
@@ -4,17 +4,14 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<% data.new_style_struct("Column", inherited=False) %>
-
 ${helpers.predefined_type(
     "column-width",
     "length::NonNegativeLengthOrAuto",
     "computed::length::NonNegativeLengthOrAuto::auto()",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
     initial_specified_value="specified::length::NonNegativeLengthOrAuto::auto()",
     animation_value_type="NonNegativeLengthOrAuto",
-    servo_2013_pref="layout.columns.enabled",
+    servo_pref="layout.columns.enabled",
     spec="https://drafts.csswg.org/css-multicol/#propdef-column-width",
     servo_restyle_damage="rebuild_and_reflow",
     affects="layout",
@@ -24,10 +21,9 @@ ${helpers.predefined_type(
     "column-count",
     "ColumnCount",
     "computed::ColumnCount::auto()",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
     initial_specified_value="specified::ColumnCount::auto()",
-    servo_2013_pref="layout.columns.enabled",
+    servo_pref="layout.columns.enabled",
     animation_value_type="AnimatedColumnCount",
     spec="https://drafts.csswg.org/css-multicol/#propdef-column-count",
     servo_restyle_damage="rebuild_and_reflow",
@@ -71,7 +67,8 @@ ${helpers.predefined_type(
 ${helpers.single_keyword(
     "column-span",
     "none all",
-    engines="gecko",
+    engines="gecko servo",
+    servo_pref="layout.columns.enabled",
     animation_value_type="discrete",
     gecko_enum_prefix="StyleColumnSpan",
     spec="https://drafts.csswg.org/css-multicol/#propdef-column-span",
diff --git a/servo/components/style/properties/longhands/counters.mako.rs b/servo/components/style/properties/longhands/counters.mako.rs
index 6c844c3567..5991bd416c 100644
--- a/servo/components/style/properties/longhands/counters.mako.rs
+++ b/servo/components/style/properties/longhands/counters.mako.rs
@@ -4,13 +4,11 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<% data.new_style_struct("Counters", inherited=False, gecko_name="Content") %>
-
 ${helpers.predefined_type(
     "content",
     "Content",
     "computed::Content::normal()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::Content::normal()",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-content/#propdef-content",
@@ -21,7 +19,8 @@ ${helpers.predefined_type(
 ${helpers.predefined_type(
     "counter-increment",
     "CounterIncrement",
-    engines="gecko servo-2013",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     initial_value="Default::default()",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-lists/#propdef-counter-increment",
@@ -32,7 +31,8 @@ ${helpers.predefined_type(
 ${helpers.predefined_type(
     "counter-reset",
     "CounterReset",
-    engines="gecko servo-2013",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     initial_value="Default::default()",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-lists-3/#propdef-counter-reset",
diff --git a/servo/components/style/properties/longhands/effects.mako.rs b/servo/components/style/properties/longhands/effects.mako.rs
index b301aab5dd..742844a670 100644
--- a/servo/components/style/properties/longhands/effects.mako.rs
+++ b/servo/components/style/properties/longhands/effects.mako.rs
@@ -4,14 +4,11 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-// Box-shadow, etc.
-<% data.new_style_struct("Effects", inherited=False) %>
-
 ${helpers.predefined_type(
     "opacity",
     "Opacity",
     "1.0",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     animation_value_type="ComputedValue",
     flags="CAN_ANIMATE_ON_COMPOSITOR",
     spec="https://drafts.csswg.org/css-color/#transparency",
@@ -23,8 +20,8 @@ ${helpers.predefined_type(
     "box-shadow",
     "BoxShadow",
     None,
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     vector=True,
     simple_vector_bindings=True,
     animation_value_type="AnimatedBoxShadowList",
@@ -39,7 +36,7 @@ ${helpers.predefined_type(
     "clip",
     "ClipRectOrAuto",
     "computed::ClipRectOrAuto::auto()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     animation_value_type="ComputedValue",
     boxed=True,
     allow_quirks="Yes",
@@ -51,7 +48,7 @@ ${helpers.predefined_type(
     "filter",
     "Filter",
     None,
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     vector=True,
     simple_vector_bindings=True,
     gecko_ffi_name="mFilters",
@@ -84,7 +81,7 @@ ${helpers.single_keyword(
     """normal multiply screen overlay darken lighten color-dodge
     color-burn hard-light soft-light difference exclusion hue
     saturation color luminosity plus-lighter""",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     gecko_enum_prefix="StyleBlend",
     animation_value_type="discrete",
     spec="https://drafts.fxtf.org/compositing/#propdef-mix-blend-mode",
diff --git a/servo/components/style/properties/longhands/font.mako.rs b/servo/components/style/properties/longhands/font.mako.rs
index 4583de0bd7..3f7a2f0657 100644
--- a/servo/components/style/properties/longhands/font.mako.rs
+++ b/servo/components/style/properties/longhands/font.mako.rs
@@ -3,14 +3,12 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
-<% from data import Method, to_camel_case, to_rust_ident, to_camel_case_lower, SYSTEM_FONT_LONGHANDS %>
-
-<% data.new_style_struct("Font", inherited=True) %>
+<% from data import SYSTEM_FONT_LONGHANDS %>
 
 ${helpers.predefined_type(
     "font-family",
     "FontFamily",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_value="computed::FontFamily::serif()",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-fonts/#propdef-font-family",
@@ -21,7 +19,7 @@ ${helpers.predefined_type(
 ${helpers.predefined_type(
     "font-style",
     "FontStyle",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_value="computed::FontStyle::normal()",
     initial_specified_value="specified::FontStyle::normal()",
     animation_value_type="FontStyle",
@@ -39,7 +37,7 @@ ${helpers.predefined_type(
 ${helpers.single_keyword(
     "font-variant-caps",
     "normal small-caps",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     extra_gecko_values="all-small-caps petite-caps all-petite-caps unicase titling-caps",
     gecko_constant_prefix="NS_FONT_VARIANT_CAPS",
     gecko_ffi_name="mFont.variantCaps",
@@ -53,7 +51,7 @@ ${helpers.single_keyword(
 ${helpers.predefined_type(
     "font-weight",
     "FontWeight",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_value="computed::FontWeight::normal()",
     initial_specified_value="specified::FontWeight::normal()",
     animation_value_type="Number",
@@ -65,7 +63,7 @@ ${helpers.predefined_type(
 ${helpers.predefined_type(
     "font-size",
     "FontSize",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_value="computed::FontSize::medium()",
     initial_specified_value="specified::FontSize::medium()",
     animation_value_type="NonNegativeLength",
@@ -137,7 +135,7 @@ ${helpers.predefined_type(
 ${helpers.predefined_type(
     "font-stretch",
     "FontStretch",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_value="computed::FontStretch::hundred()",
     initial_specified_value="specified::FontStretch::normal()",
     animation_value_type="Percentage",
@@ -354,7 +352,7 @@ ${helpers.predefined_type(
     "line-height",
     "LineHeight",
     "computed::LineHeight::normal()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     animation_value_type="LineHeight",
     spec="https://drafts.csswg.org/css2/visudet.html#propdef-line-height",
     servo_restyle_damage="reflow",
diff --git a/servo/components/style/properties/longhands/inherited_box.mako.rs b/servo/components/style/properties/longhands/inherited_box.mako.rs
index 7fd94d1a1f..add367798b 100644
--- a/servo/components/style/properties/longhands/inherited_box.mako.rs
+++ b/servo/components/style/properties/longhands/inherited_box.mako.rs
@@ -4,13 +4,11 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<% data.new_style_struct("InheritedBox", inherited=True, gecko_name="Visibility") %>
-
 // TODO: collapse. Well, do tables first.
 ${helpers.single_keyword(
     "visibility",
     "visible hidden collapse",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     gecko_ffi_name="mVisible",
     animation_value_type="ComputedValue",
     spec="https://drafts.csswg.org/css-box/#propdef-visibility",
@@ -23,13 +21,12 @@ ${helpers.single_keyword(
 ${helpers.single_keyword(
     "writing-mode",
     "horizontal-tb vertical-rl vertical-lr",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     extra_gecko_values="sideways-rl sideways-lr",
     gecko_aliases="lr=horizontal-tb lr-tb=horizontal-tb \
                          rl=horizontal-tb rl-tb=horizontal-tb \
                          tb=vertical-rl   tb-rl=vertical-rl",
-    servo_2013_pref="layout.writing-mode.enabled",
-    servo_2020_pref="layout.writing-mode.enabled",
+    servo_pref="layout.writing-mode.enabled",
     animation_value_type="none",
     spec="https://drafts.csswg.org/css-writing-modes/#propdef-writing-mode",
     gecko_enum_prefix="StyleWritingModeProperty",
@@ -40,8 +37,8 @@ ${helpers.single_keyword(
 ${helpers.single_keyword(
     "direction",
     "ltr rtl",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     animation_value_type="none",
     spec="https://drafts.csswg.org/css-writing-modes/#propdef-direction",
     gecko_enum_prefix="StyleDirection",
@@ -88,7 +85,7 @@ ${helpers.predefined_type(
     "image-rendering",
     "ImageRendering",
     "computed::ImageRendering::Auto",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-images/#propdef-image-rendering",
     animation_value_type="discrete",
     affects="paint",
diff --git a/servo/components/style/properties/longhands/inherited_svg.mako.rs b/servo/components/style/properties/longhands/inherited_svg.mako.rs
index 90443f962a..d01d5a4a80 100644
--- a/servo/components/style/properties/longhands/inherited_svg.mako.rs
+++ b/servo/components/style/properties/longhands/inherited_svg.mako.rs
@@ -4,10 +4,6 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-// SVG 2
-// https://svgwg.org/svg2-draft/
-<% data.new_style_struct("InheritedSVG", inherited=True, gecko_name="SVG") %>
-
 // Section 10 - Text
 
 ${helpers.single_keyword(
diff --git a/servo/components/style/properties/longhands/inherited_table.mako.rs b/servo/components/style/properties/longhands/inherited_table.mako.rs
index 7eb42a6eb2..c7ada525b8 100644
--- a/servo/components/style/properties/longhands/inherited_table.mako.rs
+++ b/servo/components/style/properties/longhands/inherited_table.mako.rs
@@ -4,12 +4,11 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<% data.new_style_struct("InheritedTable", inherited=True, gecko_name="TableBorder") %>
-
 ${helpers.single_keyword(
     "border-collapse",
     "separate collapse",
-    engines="gecko servo-2013",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     gecko_enum_prefix="StyleBorderCollapse",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-tables/#propdef-border-collapse",
@@ -20,7 +19,8 @@ ${helpers.single_keyword(
 ${helpers.single_keyword(
     "empty-cells",
     "show hide",
-    engines="gecko servo-2013",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     gecko_enum_prefix="StyleEmptyCells",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-tables/#propdef-empty-cells",
@@ -32,7 +32,8 @@ ${helpers.predefined_type(
     "caption-side",
     "table::CaptionSide",
     "computed::table::CaptionSide::Top",
-    engines="gecko servo-2013",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-tables/#propdef-caption-side",
     servo_restyle_damage="rebuild_and_reflow",
@@ -43,8 +44,7 @@ ${helpers.predefined_type(
     "border-spacing",
     "BorderSpacing",
     "computed::BorderSpacing::zero()",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
     animation_value_type="BorderSpacing",
     boxed=True,
     spec="https://drafts.csswg.org/css-tables/#propdef-border-spacing",
diff --git a/servo/components/style/properties/longhands/inherited_text.mako.rs b/servo/components/style/properties/longhands/inherited_text.mako.rs
index 544ba99bf7..c6ad907b23 100644
--- a/servo/components/style/properties/longhands/inherited_text.mako.rs
+++ b/servo/components/style/properties/longhands/inherited_text.mako.rs
@@ -3,14 +3,12 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
-<% from data import Keyword %>
-<% data.new_style_struct("InheritedText", inherited=True, gecko_name="Text") %>
 
 ${helpers.predefined_type(
     "color",
     "ColorPropertyValue",
     "crate::color::AbsoluteColor::BLACK",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     animation_value_type="AbsoluteColor",
     ignored_when_colors_disabled="True",
     spec="https://drafts.csswg.org/css-color/#color",
@@ -23,7 +21,8 @@ ${helpers.predefined_type(
     "text-transform",
     "TextTransform",
     "computed::TextTransform::none()",
-    engines="gecko servo-2013",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-text/#propdef-text-transform",
     servo_restyle_damage="rebuild_and_reflow",
@@ -58,8 +57,7 @@ ${helpers.predefined_type(
     "text-indent",
     "TextIndent",
     "computed::TextIndent::zero()",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
     animation_value_type="ComputedValue",
     spec="https://drafts.csswg.org/css-text/#propdef-text-indent",
     servo_restyle_damage = "reflow",
@@ -72,8 +70,8 @@ ${helpers.predefined_type(
     "overflow-wrap",
     "OverflowWrap",
     "computed::OverflowWrap::Normal",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-text/#propdef-overflow-wrap",
     aliases="word-wrap",
@@ -85,8 +83,8 @@ ${helpers.predefined_type(
     "word-break",
     "WordBreak",
     "computed::WordBreak::Normal",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-text/#propdef-word-break",
     servo_restyle_damage="rebuild_and_reflow",
@@ -97,8 +95,7 @@ ${helpers.predefined_type(
     "text-justify",
     "TextJustify",
     "computed::TextJustify::Auto",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-text/#propdef-text-justify",
     servo_restyle_damage="rebuild_and_reflow",
@@ -109,7 +106,7 @@ ${helpers.predefined_type(
     "text-align-last",
     "TextAlignLast",
     "computed::text::TextAlignLast::Auto",
-    engines="gecko",
+    engines="gecko servo",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-text/#propdef-text-align-last",
     affects="layout",
@@ -120,7 +117,7 @@ ${helpers.predefined_type(
     "text-align",
     "TextAlign",
     "computed::TextAlign::Start",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-text/#propdef-text-align",
     servo_restyle_damage = "reflow",
@@ -131,7 +128,7 @@ ${helpers.predefined_type(
     "letter-spacing",
     "LetterSpacing",
     "computed::LetterSpacing::normal()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     animation_value_type="ComputedValue",
     spec="https://drafts.csswg.org/css-text/#propdef-letter-spacing",
     servo_restyle_damage="rebuild_and_reflow",
@@ -142,7 +139,7 @@ ${helpers.predefined_type(
     "word-spacing",
     "WordSpacing",
     "computed::WordSpacing::zero()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     animation_value_type="ComputedValue",
     spec="https://drafts.csswg.org/css-text/#propdef-word-spacing",
     servo_restyle_damage="rebuild_and_reflow",
@@ -164,7 +161,8 @@ ${helpers.predefined_type(
     "text-shadow",
     "SimpleShadow",
     None,
-    engines="gecko servo-2013",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     vector=True,
     vector_animation_type="with_zero",
     animation_value_type="AnimatedTextShadowList",
@@ -304,7 +302,7 @@ ${helpers.single_keyword(
 ${helpers.single_keyword(
     "text-rendering",
     "auto optimizespeed optimizelegibility geometricprecision",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     gecko_enum_prefix="StyleTextRendering",
     animation_value_type="discrete",
     spec="https://svgwg.org/svg2-draft/painting.html#TextRenderingProperty",
diff --git a/servo/components/style/properties/longhands/inherited_ui.mako.rs b/servo/components/style/properties/longhands/inherited_ui.mako.rs
index 6cdf721336..7ee1adc602 100644
--- a/servo/components/style/properties/longhands/inherited_ui.mako.rs
+++ b/servo/components/style/properties/longhands/inherited_ui.mako.rs
@@ -4,13 +4,11 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<% data.new_style_struct("InheritedUI", inherited=True, gecko_name="UI") %>
-
 ${helpers.predefined_type(
     "cursor",
     "Cursor",
     "computed::Cursor::auto()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::Cursor::auto()",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-ui/#cursor",
@@ -23,7 +21,7 @@ ${helpers.predefined_type(
 ${helpers.single_keyword(
     "pointer-events",
     "auto none",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     animation_value_type="discrete",
     extra_gecko_values="visiblepainted visiblefill visiblestroke visible painted fill stroke all",
     spec="https://svgwg.org/svg2-draft/interact.html#PointerEventsProperty",
diff --git a/servo/components/style/properties/longhands/list.mako.rs b/servo/components/style/properties/longhands/list.mako.rs
index 619724bd32..0a3f8e36ec 100644
--- a/servo/components/style/properties/longhands/list.mako.rs
+++ b/servo/components/style/properties/longhands/list.mako.rs
@@ -4,13 +4,11 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<% data.new_style_struct("List", inherited=True) %>
-
 ${helpers.single_keyword(
     "list-style-position",
     "outside inside",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     gecko_enum_prefix="StyleListStylePosition",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-lists/#propdef-list-style-position",
@@ -24,17 +22,16 @@ ${helpers.single_keyword(
 //     upper-roman
 //
 // [1]: http://dev.w3.org/csswg/css-counter-styles/
-% if engine in ["servo-2013", "servo-2020"]:
+% if engine == "servo":
     ${helpers.single_keyword(
         "list-style-type",
-        "disc none circle square disclosure-open disclosure-closed",
-        extra_servo_2013_values="""
+        """disc none circle square disclosure-open disclosure-closed
             decimal lower-alpha upper-alpha arabic-indic bengali cambodian cjk-decimal devanagari
             gujarati gurmukhi kannada khmer lao malayalam mongolian myanmar oriya persian telugu
             thai tibetan cjk-earthly-branch cjk-heavenly-stem lower-greek hiragana hiragana-iroha
             katakana katakana-iroha
         """,
-        engines="servo-2013 servo-2020",
+        engines="servo",
         animation_value_type="discrete",
         spec="https://drafts.csswg.org/css-lists/#propdef-list-style-type",
         servo_restyle_damage="rebuild_and_reflow",
@@ -59,11 +56,12 @@ ${helpers.single_keyword(
 ${helpers.predefined_type(
     "list-style-image",
     "Image",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_value="computed::Image::None",
     initial_specified_value="specified::Image::None",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-lists/#propdef-list-style-image",
+    boxed=engine == "servo",
     servo_restyle_damage="rebuild_and_reflow",
     affects="layout",
 )}
@@ -72,7 +70,8 @@ ${helpers.predefined_type(
     "quotes",
     "Quotes",
     "computed::Quotes::get_initial_value()",
-    engines="gecko servo-2013",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-content/#propdef-quotes",
     servo_restyle_damage="rebuild_and_reflow",
diff --git a/servo/components/style/properties/longhands/margin.mako.rs b/servo/components/style/properties/longhands/margin.mako.rs
index b5a87f9683..1000704140 100644
--- a/servo/components/style/properties/longhands/margin.mako.rs
+++ b/servo/components/style/properties/longhands/margin.mako.rs
@@ -4,7 +4,6 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 <% from data import ALL_SIDES, DEFAULT_RULES_AND_PAGE, maybe_moz_logical_alias %>
-<% data.new_style_struct("Margin", inherited=False) %>
 
 % for side in ALL_SIDES:
     <%
@@ -16,7 +15,7 @@
         "margin-%s" % side[0],
         "LengthPercentageOrAuto",
         "computed::LengthPercentageOrAuto::zero()",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         aliases=maybe_moz_logical_alias(engine, side, "-moz-margin-%s"),
         allow_quirks="No" if side[1] else "Yes",
         animation_value_type="ComputedValue",
diff --git a/servo/components/style/properties/longhands/outline.mako.rs b/servo/components/style/properties/longhands/outline.mako.rs
index 8e7f956bf5..d366cbc996 100644
--- a/servo/components/style/properties/longhands/outline.mako.rs
+++ b/servo/components/style/properties/longhands/outline.mako.rs
@@ -3,18 +3,12 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
-<% from data import Method %>
 
-<% data.new_style_struct("Outline",
-                         inherited=False,
-                         additional_methods=[Method("outline_has_nonzero_width", "bool")]) %>
-
-// TODO(pcwalton): `invert`
 ${helpers.predefined_type(
     "outline-color",
     "Color",
     "computed_value::T::currentcolor()",
-    engines="gecko servo-2013",
+    engines="gecko servo",
     initial_specified_value="specified::Color::currentcolor()",
     animation_value_type="AnimatedColor",
     ignored_when_colors_disabled=True,
@@ -26,8 +20,7 @@ ${helpers.predefined_type(
     "outline-style",
     "OutlineStyle",
     "computed::OutlineStyle::none()",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
     initial_specified_value="specified::OutlineStyle::none()",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-ui/#propdef-outline-style",
@@ -38,8 +31,7 @@ ${helpers.predefined_type(
     "outline-width",
     "BorderSideWidth",
     "app_units::Au::from_px(3)",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
+    engines="gecko servo",
     initial_specified_value="specified::BorderSideWidth::medium()",
     animation_value_type="NonNegativeLength",
     spec="https://drafts.csswg.org/css-ui/#propdef-outline-width",
@@ -50,7 +42,7 @@ ${helpers.predefined_type(
     "outline-offset",
     "Length",
     "crate::values::computed::Length::new(0.)",
-    engines="gecko servo-2013",
+    engines="gecko servo",
     animation_value_type="ComputedValue",
     spec="https://drafts.csswg.org/css-ui/#propdef-outline-offset",
     affects="overflow",
diff --git a/servo/components/style/properties/longhands/padding.mako.rs b/servo/components/style/properties/longhands/padding.mako.rs
index a165e2cd34..d3984b71d2 100644
--- a/servo/components/style/properties/longhands/padding.mako.rs
+++ b/servo/components/style/properties/longhands/padding.mako.rs
@@ -4,7 +4,6 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 <% from data import ALL_SIDES, maybe_moz_logical_alias %>
-<% data.new_style_struct("Padding", inherited=False) %>
 
 % for side in ALL_SIDES:
     <%
@@ -16,7 +15,7 @@
         "padding-%s" % side[0],
         "NonNegativeLengthPercentage",
         "computed::NonNegativeLengthPercentage::zero()",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         aliases=maybe_moz_logical_alias(engine, side, "-moz-padding-%s"),
         animation_value_type="NonNegativeLengthPercentage",
         logical=side[1],
diff --git a/servo/components/style/properties/longhands/page.mako.rs b/servo/components/style/properties/longhands/page.mako.rs
index 86cd284e18..bb7729c722 100644
--- a/servo/components/style/properties/longhands/page.mako.rs
+++ b/servo/components/style/properties/longhands/page.mako.rs
@@ -5,8 +5,6 @@
 <%namespace name="helpers" file="/helpers.mako.rs" />
 <% from data import PAGE_RULE %>
 
-<% data.new_style_struct("Page", inherited=False) %>
-
 ${helpers.predefined_type(
     "size",
     "PageSize",
diff --git a/servo/components/style/properties/longhands/position.mako.rs b/servo/components/style/properties/longhands/position.mako.rs
index fb68baa6b4..e71803e026 100644
--- a/servo/components/style/properties/longhands/position.mako.rs
+++ b/servo/components/style/properties/longhands/position.mako.rs
@@ -2,19 +2,16 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-<%! from data import to_rust_ident %>
 <%namespace name="helpers" file="/helpers.mako.rs" />
 <% from data import ALL_SIZES, PHYSICAL_SIDES, LOGICAL_SIDES %>
 
-<% data.new_style_struct("Position", inherited=False) %>
-
 // "top" / "left" / "bottom" / "right"
 % for side in PHYSICAL_SIDES:
     ${helpers.predefined_type(
         side,
         "LengthPercentageOrAuto",
         "computed::LengthPercentageOrAuto::auto()",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         spec="https://www.w3.org/TR/CSS2/visuren.html#propdef-%s" % side,
         animation_value_type="ComputedValue",
         allow_quirks="Yes",
@@ -29,7 +26,7 @@
         "inset-%s" % side,
         "LengthPercentageOrAuto",
         "computed::LengthPercentageOrAuto::auto()",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         spec="https://drafts.csswg.org/css-logical-props/#propdef-inset-%s" % side,
         animation_value_type="ComputedValue",
         logical=True,
@@ -42,7 +39,7 @@ ${helpers.predefined_type(
     "z-index",
     "ZIndex",
     "computed::ZIndex::auto()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     spec="https://www.w3.org/TR/CSS2/visuren.html#z-index",
     animation_value_type="ComputedValue",
     affects="paint",
@@ -55,8 +52,8 @@ ${helpers.predefined_type(
 ${helpers.single_keyword(
     "flex-direction",
     "row row-reverse column column-reverse",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.flexbox.enabled",
+    engines="gecko servo",
+    servo_pref="layout.flexbox.enabled",
     spec="https://drafts.csswg.org/css-flexbox/#flex-direction-property",
     extra_prefixes="webkit",
     animation_value_type="discrete",
@@ -68,8 +65,8 @@ ${helpers.single_keyword(
 ${helpers.single_keyword(
     "flex-wrap",
     "nowrap wrap wrap-reverse",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.flexbox.enabled",
+    engines="gecko servo",
+    servo_pref="layout.flexbox.enabled",
     spec="https://drafts.csswg.org/css-flexbox/#flex-wrap-property",
     extra_prefixes="webkit",
     animation_value_type="discrete",
@@ -78,12 +75,13 @@ ${helpers.single_keyword(
     affects="layout",
 )}
 
-% if engine == "servo-2013":
+% if engine in "servo":
     // FIXME: Update Servo to support the same Syntax as Gecko.
     ${helpers.single_keyword(
         "justify-content",
         "flex-start stretch flex-end center space-between space-around",
-        engines="servo-2013",
+        engines="servo",
+        servo_pref="layout.flexbox.enabled",
         extra_prefixes="webkit",
         spec="https://drafts.csswg.org/css-align/#propdef-justify-content",
         animation_value_type="discrete",
@@ -117,12 +115,13 @@ ${helpers.single_keyword(
     )}
 % endif
 
-% if engine in ["servo-2013", "servo-2020"]:
+% if engine == "servo":
     // FIXME: Update Servo to support the same Syntax as Gecko.
     ${helpers.single_keyword(
         "align-content",
         "stretch flex-start flex-end center space-between space-around",
-        engines="servo-2013",
+        engines="servo",
+        servo_pref="layout.flexbox.enabled",
         extra_prefixes="webkit",
         spec="https://drafts.csswg.org/css-align/#propdef-align-content",
         animation_value_type="discrete",
@@ -133,8 +132,8 @@ ${helpers.single_keyword(
     ${helpers.single_keyword(
         "align-items",
         "stretch flex-start flex-end center baseline",
-        engines="servo-2013 servo-2020",
-        servo_2020_pref="layout.flexbox.enabled",
+        engines="servo",
+        servo_pref="layout.flexbox.enabled",
         extra_prefixes="webkit",
         spec="https://drafts.csswg.org/css-flexbox/#align-items-property",
         animation_value_type="discrete",
@@ -195,8 +194,8 @@ ${helpers.predefined_type(
     "flex-grow",
     "NonNegativeNumber",
     "From::from(0.0)",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.flexbox.enabled",
+    engines="gecko servo",
+    servo_pref="layout.flexbox.enabled",
     spec="https://drafts.csswg.org/css-flexbox/#flex-grow-property",
     extra_prefixes="webkit",
     animation_value_type="NonNegativeNumber",
@@ -208,8 +207,8 @@ ${helpers.predefined_type(
     "flex-shrink",
     "NonNegativeNumber",
     "From::from(1.0)",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.flexbox.enabled",
+    engines="gecko servo",
+    servo_pref="layout.flexbox.enabled",
     spec="https://drafts.csswg.org/css-flexbox/#flex-shrink-property",
     extra_prefixes="webkit",
     animation_value_type="NonNegativeNumber",
@@ -218,13 +217,13 @@ ${helpers.predefined_type(
 )}
 
 // https://drafts.csswg.org/css-align/#align-self-property
-% if engine in ["servo-2013", "servo-2020"]:
+% if engine == "servo":
     // FIXME: Update Servo to support the same syntax as Gecko.
     ${helpers.single_keyword(
         "align-self",
         "auto stretch flex-start flex-end center baseline",
-        engines="servo-2013 servo-2020",
-        servo_2020_pref="layout.flexbox.enabled",
+        engines="servo",
+        servo_pref="layout.flexbox.enabled",
         extra_prefixes="webkit",
         spec="https://drafts.csswg.org/css-flexbox/#propdef-align-self",
         animation_value_type="discrete",
@@ -260,8 +259,8 @@ ${helpers.predefined_type(
     "order",
     "Integer",
     "0",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.flexbox.enabled",
+    engines="gecko servo",
+    servo_pref="layout.flexbox.enabled",
     extra_prefixes="webkit",
     animation_value_type="ComputedValue",
     spec="https://drafts.csswg.org/css-flexbox/#order-property",
@@ -273,8 +272,8 @@ ${helpers.predefined_type(
     "flex-basis",
     "FlexBasis",
     "computed::FlexBasis::auto()",
-    engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.flexbox.enabled",
+    engines="gecko servo",
+    servo_pref="layout.flexbox.enabled",
     spec="https://drafts.csswg.org/css-flexbox/#flex-basis-property",
     extra_prefixes="webkit",
     animation_value_type="FlexBasis",
@@ -294,7 +293,7 @@ ${helpers.predefined_type(
         size,
         "Size",
         "computed::Size::auto()",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         logical=logical,
         logical_group="size",
         allow_quirks="No" if logical else "Yes",
@@ -308,7 +307,7 @@ ${helpers.predefined_type(
         "min-%s" % size,
         "Size",
         "computed::Size::auto()",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         logical=logical,
         logical_group="min-size",
         allow_quirks="No" if logical else "Yes",
@@ -321,7 +320,7 @@ ${helpers.predefined_type(
         "max-%s" % size,
         "MaxSize",
         "computed::MaxSize::none()",
-        engines="gecko servo-2013 servo-2020",
+        engines="gecko servo",
         logical=logical,
         logical_group="max-size",
         allow_quirks="No" if logical else "Yes",
@@ -335,7 +334,7 @@ ${helpers.predefined_type(
 ${helpers.single_keyword(
     "box-sizing",
     "content-box border-box",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     extra_prefixes="moz:layout.css.prefixes.box-sizing webkit",
     spec="https://drafts.csswg.org/css-ui/#propdef-box-sizing",
     gecko_enum_prefix="StyleBoxSizing",
@@ -436,9 +435,9 @@ ${helpers.predefined_type(
     "column-gap",
     "length::NonNegativeLengthPercentageOrNormal",
     "computed::length::NonNegativeLengthPercentageOrNormal::normal()",
-    engines="gecko servo-2013",
+    engines="gecko servo",
     aliases="grid-column-gap" if engine == "gecko" else "",
-    servo_2013_pref="layout.columns.enabled",
+    servo_pref="layout.columns.enabled",
     spec="https://drafts.csswg.org/css-align-3/#propdef-column-gap",
     animation_value_type="NonNegativeLengthPercentageOrNormal",
     servo_restyle_damage="reflow",
@@ -462,7 +461,8 @@ ${helpers.predefined_type(
     "aspect-ratio",
     "AspectRatio",
     "computed::AspectRatio::auto()",
-    engines="gecko servo-2013",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     animation_value_type="ComputedValue",
     spec="https://drafts.csswg.org/css-sizing-4/#aspect-ratio",
     servo_restyle_damage="reflow",
diff --git a/servo/components/style/properties/longhands/svg.mako.rs b/servo/components/style/properties/longhands/svg.mako.rs
index 10788d4802..12998d553b 100644
--- a/servo/components/style/properties/longhands/svg.mako.rs
+++ b/servo/components/style/properties/longhands/svg.mako.rs
@@ -4,8 +4,6 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<% data.new_style_struct("SVG", inherited=False, gecko_name="SVGReset") %>
-
 ${helpers.single_keyword(
     "vector-effect",
     "none non-scaling-stroke",
diff --git a/servo/components/style/properties/longhands/table.mako.rs b/servo/components/style/properties/longhands/table.mako.rs
index 3a756636ad..059838bac1 100644
--- a/servo/components/style/properties/longhands/table.mako.rs
+++ b/servo/components/style/properties/longhands/table.mako.rs
@@ -4,12 +4,11 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<% data.new_style_struct("Table", inherited=False) %>
-
 ${helpers.single_keyword(
     "table-layout",
     "auto fixed",
-    engines="gecko servo-2013",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     gecko_ffi_name="mLayoutStrategy",
     animation_value_type="discrete",
     gecko_enum_prefix="StyleTableLayout",
diff --git a/servo/components/style/properties/longhands/text.mako.rs b/servo/components/style/properties/longhands/text.mako.rs
index 0ee8ba3168..68b8ff3ceb 100644
--- a/servo/components/style/properties/longhands/text.mako.rs
+++ b/servo/components/style/properties/longhands/text.mako.rs
@@ -3,15 +3,13 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
-<% from data import Method %>
-
-<% data.new_style_struct("Text", inherited=False, gecko_name="TextReset") %>
 
 ${helpers.predefined_type(
     "text-overflow",
     "TextOverflow",
     "computed::TextOverflow::get_initial_value()",
-    engines="gecko servo-2013",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     animation_value_type="discrete",
     boxed=True,
     spec="https://drafts.csswg.org/css-ui/#propdef-text-overflow",
@@ -22,7 +20,8 @@ ${helpers.predefined_type(
 ${helpers.single_keyword(
     "unicode-bidi",
     "normal embed isolate bidi-override isolate-override plaintext",
-    engines="gecko servo-2013",
+    engines="gecko servo",
+    servo_pref="layout.legacy_layout",
     gecko_enum_prefix="StyleUnicodeBidi",
     animation_value_type="none",
     spec="https://drafts.csswg.org/css-writing-modes/#propdef-unicode-bidi",
@@ -34,7 +33,7 @@ ${helpers.predefined_type(
     "text-decoration-line",
     "TextDecorationLine",
     "specified::TextDecorationLine::none()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::TextDecorationLine::none()",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-text-decor/#propdef-text-decoration-line",
@@ -45,7 +44,7 @@ ${helpers.predefined_type(
 ${helpers.single_keyword(
     "text-decoration-style",
     "solid double dotted dashed wavy -moz-none",
-    engines="gecko servo-2020",
+    engines="gecko servo",
     gecko_enum_prefix="StyleTextDecorationStyle",
     animation_value_type="discrete",
     spec="https://drafts.csswg.org/css-text-decor/#propdef-text-decoration-style",
@@ -56,7 +55,7 @@ ${helpers.predefined_type(
     "text-decoration-color",
     "Color",
     "computed_value::T::currentcolor()",
-    engines="gecko servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::Color::currentcolor()",
     animation_value_type="AnimatedColor",
     ignored_when_colors_disabled=True,
diff --git a/servo/components/style/properties/longhands/ui.mako.rs b/servo/components/style/properties/longhands/ui.mako.rs
index 58006e0d65..762cb64e9a 100644
--- a/servo/components/style/properties/longhands/ui.mako.rs
+++ b/servo/components/style/properties/longhands/ui.mako.rs
@@ -3,11 +3,7 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
-<% from data import DEFAULT_RULES_EXCEPT_KEYFRAME, Method %>
-
-// CSS Basic User Interface Module Level 1
-// https://drafts.csswg.org/css-ui-3/
-<% data.new_style_struct("UI", inherited=False, gecko_name="UIReset") %>
+<% from data import DEFAULT_RULES_EXCEPT_KEYFRAME %>
 
 // TODO spec says that UAs should not support this
 // we should probably remove from gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=1328331)
@@ -145,7 +141,7 @@ ${helpers.predefined_type(
     "transition-duration",
     "Time",
     "computed::Time::zero()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::Time::zero()",
     parse_method="parse_non_negative",
     vector=True,
@@ -160,7 +156,7 @@ ${helpers.predefined_type(
     "transition-timing-function",
     "TimingFunction",
     "computed::TimingFunction::ease()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::TimingFunction::ease()",
     vector=True,
     need_index=True,
@@ -174,7 +170,7 @@ ${helpers.predefined_type(
     "transition-property",
     "TransitionProperty",
     "computed::TransitionProperty::all()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::TransitionProperty::all()",
     vector=True,
     none_value="computed::TransitionProperty::none()",
@@ -189,7 +185,7 @@ ${helpers.predefined_type(
     "transition-delay",
     "Time",
     "computed::Time::zero()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::Time::zero()",
     vector=True,
     need_index=True,
@@ -219,7 +215,7 @@ ${helpers.predefined_type(
     "animation-name",
     "AnimationName",
     "computed::AnimationName::none()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::AnimationName::none()",
     vector=True,
     need_index=True,
@@ -234,7 +230,7 @@ ${helpers.predefined_type(
     "animation-duration",
     "Time",
     "computed::Time::zero()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::Time::zero()",
     parse_method="parse_non_negative",
     vector=True,
@@ -251,7 +247,7 @@ ${helpers.predefined_type(
     "animation-timing-function",
     "TimingFunction",
     "computed::TimingFunction::ease()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::TimingFunction::ease()",
     vector=True,
     need_index=True,
@@ -265,7 +261,7 @@ ${helpers.predefined_type(
     "animation-iteration-count",
     "AnimationIterationCount",
     "computed::AnimationIterationCount::one()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::AnimationIterationCount::one()",
     vector=True,
     need_index=True,
@@ -280,7 +276,7 @@ ${helpers.predefined_type(
     "animation-direction",
     "AnimationDirection",
     "computed::AnimationDirection::Normal",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::AnimationDirection::Normal",
     vector=True,
     need_index=True,
@@ -295,7 +291,7 @@ ${helpers.predefined_type(
     "animation-play-state",
     "AnimationPlayState",
     "computed::AnimationPlayState::Running",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="computed::AnimationPlayState::Running",
     vector=True,
     need_index=True,
@@ -310,7 +306,7 @@ ${helpers.predefined_type(
     "animation-fill-mode",
     "AnimationFillMode",
     "computed::AnimationFillMode::None",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="computed::AnimationFillMode::None",
     vector=True,
     need_index=True,
@@ -325,12 +321,13 @@ ${helpers.predefined_type(
     "animation-composition",
     "AnimationComposition",
     "computed::AnimationComposition::Replace",
-    engines="gecko",
+    engines="gecko servo",
     initial_specified_value="computed::AnimationComposition::Replace",
     vector=True,
     need_index=True,
     animation_value_type="none",
     gecko_pref="layout.css.animation-composition.enabled",
+    servo_pref="layout.unimplemented",
     spec="https://drafts.csswg.org/css-animations-2/#animation-composition",
     affects="",
 )}
@@ -339,7 +336,7 @@ ${helpers.predefined_type(
     "animation-delay",
     "Time",
     "computed::Time::zero()",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     initial_specified_value="specified::Time::zero()",
     vector=True,
     need_index=True,
@@ -354,7 +351,8 @@ ${helpers.predefined_type(
     "animation-timeline",
     "AnimationTimeline",
     "computed::AnimationTimeline::auto()",
-    engines="gecko",
+    engines="gecko servo",
+    servo_pref="layout.unimplemented",
     initial_specified_value="specified::AnimationTimeline::auto()",
     vector=True,
     need_index=True,
diff --git a/servo/components/style/properties/longhands/xul.mako.rs b/servo/components/style/properties/longhands/xul.mako.rs
index 8974ac30dc..f9de8eb239 100644
--- a/servo/components/style/properties/longhands/xul.mako.rs
+++ b/servo/components/style/properties/longhands/xul.mako.rs
@@ -3,10 +3,6 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
-<% from data import Method %>
-
-// Non-standard properties that Gecko uses for XUL elements.
-<% data.new_style_struct("XUL", inherited=False) %>
 
 ${helpers.single_keyword(
     "-moz-box-align",
diff --git a/servo/components/style/properties/mod.rs b/servo/components/style/properties/mod.rs
index 7adb6d4ae6..4a08d67f77 100644
--- a/servo/components/style/properties/mod.rs
+++ b/servo/components/style/properties/mod.rs
@@ -17,12 +17,6 @@ pub use self::generated::*;
 #[deny(missing_docs)]
 pub mod generated {
     include!(concat!(env!("OUT_DIR"), "/properties.rs"));
-
-    #[cfg(feature = "gecko")]
-    #[allow(unsafe_code, missing_docs)]
-    pub mod gecko {
-        include!(concat!(env!("OUT_DIR"), "/gecko_properties.rs"));
-    }
 }
 
 use crate::custom_properties::{self, ComputedCustomProperties};
@@ -1040,7 +1034,7 @@ impl<'a> PropertyDeclarationId<'a> {
     pub fn is_discrete_animatable(&self) -> bool {
         match self {
             Self::Longhand(longhand) => longhand.is_discrete_animatable(),
-            // TODO(bug 1846516): Refine this?
+            // TODO(bug 1885995): Refine this.
             Self::Custom(_) => true,
         }
     }
diff --git a/servo/components/style/properties/properties.mako.rs b/servo/components/style/properties/properties.mako.rs
index b08314d7d5..e438967c35 100644
--- a/servo/components/style/properties/properties.mako.rs
+++ b/servo/components/style/properties/properties.mako.rs
@@ -87,10 +87,19 @@ macro_rules! expanded {
 #[allow(missing_docs)]
 pub mod longhands {
     % for style_struct in data.style_structs:
-    include!("${repr(os.path.join(OUT_DIR, 'longhands/{}.rs'.format(style_struct.name_lower)))[1:-1]}");
+    <% data.current_style_struct = style_struct %>
+    <%include file="/longhands/${style_struct.name_lower}.mako.rs" />
     % endfor
 }
 
+
+#[cfg(feature = "gecko")]
+#[allow(unsafe_code, missing_docs)]
+pub mod gecko {
+    <%include file="/gecko.mako.rs" />
+}
+
+
 macro_rules! unwrap_or_initial {
     ($prop: ident) => (unwrap_or_initial!($prop, $prop));
     ($prop: ident, $expr: expr) =>
@@ -107,7 +116,7 @@ pub mod shorthands {
     use crate::values::specified;
 
     % for style_struct in data.style_structs:
-    include!("${repr(os.path.join(OUT_DIR, 'shorthands/{}.rs'.format(style_struct.name_lower)))[1:-1]}");
+    <%include file="/shorthands/${style_struct.name_lower}.mako.rs" />
     % endfor
 
     // We didn't define the 'all' shorthand using the regular helpers:shorthand
@@ -142,7 +151,7 @@ pub mod shorthands {
         data.declare_shorthand(
             "all",
             logical_longhands + other_longhands,
-            engines="gecko servo-2013 servo-2020",
+            engines="gecko servo",
             spec="https://drafts.csswg.org/css-cascade-3/#all-shorthand"
         )
         ALL_SHORTHAND_LEN = len(logical_longhands) + len(other_longhands);
@@ -505,8 +514,7 @@ impl NonCustomPropertyId {
                 }] = [
                     % for property in data.longhands + data.shorthands + data.all_aliases():
                         <%
-                            attrs = {"servo-2013": "servo_2013_pref", "servo-2020": "servo_2020_pref"}
-                            pref = getattr(property, attrs[engine])
+                            pref = getattr(property, "servo_pref")
                         %>
                         % if pref:
                             Some("${pref}"),
@@ -2482,7 +2490,7 @@ impl<'a> StyleBuilder<'a> {
     }
     % endif
 
-    % if not property.is_vector or property.simple_vector_bindings or engine in ["servo-2013", "servo-2020"]:
+    % if not property.is_vector or property.simple_vector_bindings or engine == "servo":
     /// Set the `${property.ident}` to the computed value `value`.
     #[allow(non_snake_case)]
     pub fn set_${property.ident}(
@@ -2736,7 +2744,13 @@ impl<'a> StyleBuilder<'a> {
         if matches!(line_height, computed::LineHeight::Normal) {
             self.add_flags(flag);
         }
-        device.calc_line_height(&font, writing_mode, None)
+        let lh = device.calc_line_height(&font, writing_mode, None);
+        if line_height_base == LineHeightBase::InheritedStyle {
+            // Apply our own zoom if our style source is the parent style.
+            computed::NonNegativeLength::new(self.get_box().clone_zoom().zoom(lh.px()))
+        } else {
+            lh
+        }
     }
 
     /// And access to inherited style structs.
@@ -2932,7 +2946,7 @@ const_assert!(std::mem::size_of::<longhands::${longhand.ident}::SpecifiedValue>(
 % endif
 % endfor
 
-% if engine in ["servo-2013", "servo-2020"]:
+% if engine == "servo":
 % for effect_name in ["repaint", "reflow_out_of_flow", "reflow", "rebuild_and_reflow_inline", "rebuild_and_reflow"]:
     macro_rules! restyle_damage_${effect_name} {
         ($old: ident, $new: ident, $damage: ident, [ $($effect:expr),* ]) => ({
diff --git a/servo/components/style/properties/shorthands/background.mako.rs b/servo/components/style/properties/shorthands/background.mako.rs
index 08838233f6..5fee5cb2b0 100644
--- a/servo/components/style/properties/shorthands/background.mako.rs
+++ b/servo/components/style/properties/shorthands/background.mako.rs
@@ -6,7 +6,7 @@
 
 // TODO: other background-* properties
 <%helpers:shorthand name="background"
-                    engines="gecko servo-2013 servo-2020"
+                    engines="gecko servo"
                     sub_properties="background-color background-position-x background-position-y background-repeat
                                     background-attachment background-image background-size background-origin
                                     background-clip"
@@ -230,7 +230,7 @@
 </%helpers:shorthand>
 
 <%helpers:shorthand name="background-position"
-                    engines="gecko servo-2013 servo-2020"
+                    engines="gecko servo"
                     flags="SHORTHAND_IN_GETCS"
                     sub_properties="background-position-x background-position-y"
                     spec="https://drafts.csswg.org/css-backgrounds-4/#the-background-position">
diff --git a/servo/components/style/properties/shorthands/border.mako.rs b/servo/components/style/properties/shorthands/border.mako.rs
index c6a87f3197..2eeb691e24 100644
--- a/servo/components/style/properties/shorthands/border.mako.rs
+++ b/servo/components/style/properties/shorthands/border.mako.rs
@@ -9,7 +9,7 @@ ${helpers.four_sides_shorthand(
     "border-color",
     "border-%s-color",
     "specified::Color::parse",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-backgrounds/#border-color",
     allow_quirks="Yes",
 )}
@@ -17,13 +17,13 @@ ${helpers.four_sides_shorthand(
 ${helpers.four_sides_shorthand(
     "border-style",
     "border-%s-style",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-backgrounds/#border-style",
 )}
 
 <%helpers:shorthand
     name="border-width"
-    engines="gecko servo-2013 servo-2020"
+    engines="gecko servo"
     sub_properties="${
         ' '.join('border-%s-width' % side
                  for side in PHYSICAL_SIDES)}"
@@ -104,7 +104,7 @@ pub fn parse_border<'i, 't>(
     %>
     <%helpers:shorthand
         name="border-${side}"
-        engines="gecko servo-2013 servo-2020"
+        engines="gecko servo"
         sub_properties="${' '.join(
             'border-%s-%s' % (side, prop)
             for prop in ['width', 'style', 'color']
@@ -139,7 +139,7 @@ pub fn parse_border<'i, 't>(
 % endfor
 
 <%helpers:shorthand name="border"
-    engines="gecko servo-2013 servo-2020"
+    engines="gecko servo"
     sub_properties="${' '.join('border-%s-%s' % (side, prop)
         for side in PHYSICAL_SIDES for prop in ['width', 'style', 'color']
         )}
@@ -232,7 +232,7 @@ pub fn parse_border<'i, 't>(
 
 <%helpers:shorthand
     name="border-radius"
-    engines="gecko servo-2013 servo-2020"
+    engines="gecko servo"
     sub_properties="${' '.join(
         'border-%s-radius' % (corner)
          for corner in ['top-left', 'top-right', 'bottom-right', 'bottom-left']
@@ -278,7 +278,8 @@ pub fn parse_border<'i, 't>(
 
 <%helpers:shorthand
     name="border-image"
-    engines="gecko servo-2013"
+    engines="gecko servo"
+    servo_pref="layout.legacy_layout",
     sub_properties="border-image-outset
         border-image-repeat border-image-slice border-image-source border-image-width"
     extra_prefixes="moz:layout.css.prefixes.border-image webkit"
@@ -402,7 +403,7 @@ pub fn parse_border<'i, 't>(
             spec = "https://drafts.csswg.org/css-logical/#propdef-border-%s-%s" % (axis, prop)
         %>
         <%helpers:shorthand
-            engines="gecko servo-2013 servo-2020"
+            engines="gecko servo"
             name="border-${axis}-${prop}"
             sub_properties="${' '.join(
                 'border-%s-%s-%s' % (axis, side, prop)
@@ -448,7 +449,7 @@ pub fn parse_border<'i, 't>(
     %>
     <%helpers:shorthand
         name="border-${axis}"
-        engines="gecko servo-2013 servo-2020"
+        engines="gecko servo"
         sub_properties="${' '.join(
             'border-%s-%s-width' % (axis, side)
             for side in ['start', 'end']
diff --git a/servo/components/style/properties/shorthands/box.mako.rs b/servo/components/style/properties/shorthands/box.mako.rs
index f644687dc0..078a511ae9 100644
--- a/servo/components/style/properties/shorthands/box.mako.rs
+++ b/servo/components/style/properties/shorthands/box.mako.rs
@@ -8,7 +8,7 @@ ${helpers.two_properties_shorthand(
     "overflow",
     "overflow-x",
     "overflow-y",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     flags="SHORTHAND_IN_GETCS",
     spec="https://drafts.csswg.org/css-overflow/#propdef-overflow",
 )}
@@ -159,13 +159,7 @@ ${helpers.two_properties_shorthand(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Longhands, ParseError<'i>> {
-        let offset_position =
-            if static_prefs::pref!("layout.css.motion-path-offset-position.enabled") {
-                input.try_parse(|i| OffsetPosition::parse(context, i)).ok()
-            } else {
-                None
-            };
-
+        let offset_position = input.try_parse(|i| OffsetPosition::parse(context, i)).ok();
         let offset_path = input.try_parse(|i| OffsetPath::parse(context, i)).ok();
 
         // Must have one of [offset-position, offset-path].
@@ -212,24 +206,19 @@ ${helpers.two_properties_shorthand(
 
     impl<'a> ToCss for LonghandsToSerialize<'a>  {
         fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result where W: fmt::Write {
-            if let Some(offset_position) = self.offset_position {
-                // The basic concept is: we must serialize offset-position or offset-path group.
-                // offset-path group means "offset-path offset-distance offset-rotate".
-                let must_serialize_path = *self.offset_path != OffsetPath::None
-                    || (!self.offset_distance.is_zero() || !self.offset_rotate.is_auto());
-                let position_is_default = matches!(offset_position, OffsetPosition::Normal);
-                if !position_is_default || !must_serialize_path {
-                    offset_position.to_css(dest)?;
-                }
+            // The basic concept is: we must serialize offset-position or offset-path group.
+            // offset-path group means "offset-path offset-distance offset-rotate".
+            let must_serialize_path = *self.offset_path != OffsetPath::None
+                || (!self.offset_distance.is_zero() || !self.offset_rotate.is_auto());
+            let position_is_default = matches!(self.offset_position, OffsetPosition::Normal);
+            if !position_is_default || !must_serialize_path {
+                self.offset_position.to_css(dest)?;
+            }
 
-                if must_serialize_path {
-                    if !position_is_default {
-                        dest.write_char(' ')?;
-                    }
-                    self.offset_path.to_css(dest)?;
+            if must_serialize_path {
+                if !position_is_default {
+                    dest.write_char(' ')?;
                 }
-            } else {
-                // If the pref is off, we always show offset-path.
                 self.offset_path.to_css(dest)?;
             }
 
diff --git a/servo/components/style/properties/shorthands/column.mako.rs b/servo/components/style/properties/shorthands/column.mako.rs
index 3740775a7e..4cf9a8d786 100644
--- a/servo/components/style/properties/shorthands/column.mako.rs
+++ b/servo/components/style/properties/shorthands/column.mako.rs
@@ -5,9 +5,9 @@
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
 <%helpers:shorthand name="columns"
-                    engines="gecko servo-2013"
+                    engines="gecko servo"
                     sub_properties="column-width column-count"
-                    servo_2013_pref="layout.columns.enabled",
+                    servo_pref="layout.columns.enabled"
                     spec="https://drafts.csswg.org/css-multicol/#propdef-columns">
     use crate::properties::longhands::{column_count, column_width};
 
diff --git a/servo/components/style/properties/shorthands/counters.mako.rs b/servo/components/style/properties/shorthands/counters.mako.rs
new file mode 100644
index 0000000000..daa3e8897c
--- /dev/null
+++ b/servo/components/style/properties/shorthands/counters.mako.rs
@@ -0,0 +1,3 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
diff --git a/servo/components/style/properties/shorthands/effects.mako.rs b/servo/components/style/properties/shorthands/effects.mako.rs
new file mode 100644
index 0000000000..daa3e8897c
--- /dev/null
+++ b/servo/components/style/properties/shorthands/effects.mako.rs
@@ -0,0 +1,3 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
diff --git a/servo/components/style/properties/shorthands/font.mako.rs b/servo/components/style/properties/shorthands/font.mako.rs
index 17dcf9d926..aaf0895aa5 100644
--- a/servo/components/style/properties/shorthands/font.mako.rs
+++ b/servo/components/style/properties/shorthands/font.mako.rs
@@ -7,7 +7,7 @@
 
 <%helpers:shorthand
     name="font"
-    engines="gecko servo-2013 servo-2020"
+    engines="gecko servo"
     sub_properties="
         font-style
         font-variant-caps
@@ -321,7 +321,8 @@
 </%helpers:shorthand>
 
 <%helpers:shorthand name="font-variant"
-                    engines="gecko servo-2013"
+                    engines="gecko servo"
+                    servo_pref="layout.legacy_layout",
                     flags="SHORTHAND_IN_GETCS"
                     sub_properties="font-variant-caps
                                     ${'font-variant-alternates' if engine == 'gecko' else ''}
diff --git a/servo/components/style/properties/shorthands/inherited_box.mako.rs b/servo/components/style/properties/shorthands/inherited_box.mako.rs
new file mode 100644
index 0000000000..daa3e8897c
--- /dev/null
+++ b/servo/components/style/properties/shorthands/inherited_box.mako.rs
@@ -0,0 +1,3 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
diff --git a/servo/components/style/properties/shorthands/inherited_table.mako.rs b/servo/components/style/properties/shorthands/inherited_table.mako.rs
new file mode 100644
index 0000000000..daa3e8897c
--- /dev/null
+++ b/servo/components/style/properties/shorthands/inherited_table.mako.rs
@@ -0,0 +1,3 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
diff --git a/servo/components/style/properties/shorthands/inherited_ui.mako.rs b/servo/components/style/properties/shorthands/inherited_ui.mako.rs
new file mode 100644
index 0000000000..daa3e8897c
--- /dev/null
+++ b/servo/components/style/properties/shorthands/inherited_ui.mako.rs
@@ -0,0 +1,3 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
diff --git a/servo/components/style/properties/shorthands/list.mako.rs b/servo/components/style/properties/shorthands/list.mako.rs
index 2e234e3d8f..183c5ab5da 100644
--- a/servo/components/style/properties/shorthands/list.mako.rs
+++ b/servo/components/style/properties/shorthands/list.mako.rs
@@ -5,7 +5,7 @@
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
 <%helpers:shorthand name="list-style"
-                    engines="gecko servo-2013 servo-2020"
+                    engines="gecko servo"
                     sub_properties="list-style-position list-style-image list-style-type"
                     spec="https://drafts.csswg.org/css-lists/#propdef-list-style">
     use crate::properties::longhands::{list_style_image, list_style_position, list_style_type};
@@ -110,7 +110,11 @@
             use longhands::list_style_type::SpecifiedValue as ListStyleType;
             use longhands::list_style_image::SpecifiedValue as ListStyleImage;
             let mut have_one_non_initial_value = false;
-            if self.list_style_position != &ListStylePosition::Outside {
+            #[cfg(feature = "gecko")]
+            let position_is_initial = self.list_style_position == &ListStylePosition::Outside;
+            #[cfg(feature = "servo")]
+            let position_is_initial = matches!(self.list_style_position, None | Some(&ListStylePosition::Outside));
+            if !position_is_initial {
                 self.list_style_position.to_css(dest)?;
                 have_one_non_initial_value = true;
             }
@@ -121,7 +125,11 @@
                 self.list_style_image.to_css(dest)?;
                 have_one_non_initial_value = true;
             }
-            if self.list_style_type != &ListStyleType::disc() {
+            #[cfg(feature = "gecko")]
+            let type_is_initial = self.list_style_type == &ListStyleType::disc();
+            #[cfg(feature = "servo")]
+            let type_is_initial = self.list_style_type == &ListStyleType::Disc;
+            if !type_is_initial {
                 if have_one_non_initial_value {
                     dest.write_char(' ')?;
                 }
@@ -129,7 +137,14 @@
                 have_one_non_initial_value = true;
             }
             if !have_one_non_initial_value {
+                #[cfg(feature = "gecko")]
                 self.list_style_position.to_css(dest)?;
+                #[cfg(feature = "servo")]
+                if let Some(position) = self.list_style_position {
+                    position.to_css(dest)?;
+                } else {
+                    self.list_style_type.to_css(dest)?;
+                }
             }
             Ok(())
         }
diff --git a/servo/components/style/properties/shorthands/margin.mako.rs b/servo/components/style/properties/shorthands/margin.mako.rs
index 6b5bf7e467..ba994316a2 100644
--- a/servo/components/style/properties/shorthands/margin.mako.rs
+++ b/servo/components/style/properties/shorthands/margin.mako.rs
@@ -9,7 +9,7 @@ ${helpers.four_sides_shorthand(
     "margin",
     "margin-%s",
     "specified::LengthPercentageOrAuto::parse",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-box/#propdef-margin",
     rule_types_allowed=DEFAULT_RULES_AND_PAGE,
     allow_quirks="Yes",
@@ -20,7 +20,7 @@ ${helpers.two_properties_shorthand(
     "margin-block-start",
     "margin-block-end",
     "specified::LengthPercentageOrAuto::parse",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-logical/#propdef-margin-block"
 )}
 
@@ -29,7 +29,7 @@ ${helpers.two_properties_shorthand(
     "margin-inline-start",
     "margin-inline-end",
     "specified::LengthPercentageOrAuto::parse",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-logical/#propdef-margin-inline"
 )}
 
diff --git a/servo/components/style/properties/shorthands/outline.mako.rs b/servo/components/style/properties/shorthands/outline.mako.rs
index 6ee8ed22c9..ff77e1175e 100644
--- a/servo/components/style/properties/shorthands/outline.mako.rs
+++ b/servo/components/style/properties/shorthands/outline.mako.rs
@@ -5,7 +5,7 @@
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
 <%helpers:shorthand name="outline"
-                    engines="gecko servo-2013"
+                    engines="gecko servo"
                     sub_properties="outline-color outline-style outline-width"
                     spec="https://drafts.csswg.org/css-ui/#propdef-outline">
     use crate::properties::longhands::{outline_color, outline_width, outline_style};
diff --git a/servo/components/style/properties/shorthands/padding.mako.rs b/servo/components/style/properties/shorthands/padding.mako.rs
index 11ddfed3b1..dad0193708 100644
--- a/servo/components/style/properties/shorthands/padding.mako.rs
+++ b/servo/components/style/properties/shorthands/padding.mako.rs
@@ -8,7 +8,7 @@ ${helpers.four_sides_shorthand(
     "padding",
     "padding-%s",
     "specified::NonNegativeLengthPercentage::parse",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-box-3/#propdef-padding",
     allow_quirks="Yes",
 )}
@@ -18,7 +18,7 @@ ${helpers.two_properties_shorthand(
     "padding-block-start",
     "padding-block-end",
     "specified::NonNegativeLengthPercentage::parse",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-logical/#propdef-padding-block"
 )}
 
@@ -27,7 +27,7 @@ ${helpers.two_properties_shorthand(
     "padding-inline-start",
     "padding-inline-end",
     "specified::NonNegativeLengthPercentage::parse",
-    engines="gecko servo-2013 servo-2020",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-logical/#propdef-padding-inline"
 )}
 
diff --git a/servo/components/style/properties/shorthands/page.mako.rs b/servo/components/style/properties/shorthands/page.mako.rs
new file mode 100644
index 0000000000..daa3e8897c
--- /dev/null
+++ b/servo/components/style/properties/shorthands/page.mako.rs
@@ -0,0 +1,3 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
diff --git a/servo/components/style/properties/shorthands/position.mako.rs b/servo/components/style/properties/shorthands/position.mako.rs
index ed7df5e27a..ac09bb27d6 100644
--- a/servo/components/style/properties/shorthands/position.mako.rs
+++ b/servo/components/style/properties/shorthands/position.mako.rs
@@ -5,8 +5,8 @@
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
 <%helpers:shorthand name="flex-flow"
-                    engines="gecko servo-2013 servo-2020",
-                    servo_2020_pref="layout.flexbox.enabled",
+                    engines="gecko servo",
+                    servo_pref="layout.flexbox.enabled",
                     sub_properties="flex-direction flex-wrap"
                     extra_prefixes="webkit"
                     spec="https://drafts.csswg.org/css-flexbox/#flex-flow-property">
@@ -60,8 +60,8 @@
 </%helpers:shorthand>
 
 <%helpers:shorthand name="flex"
-                    engines="gecko servo-2013 servo-2020",
-                    servo_2020_pref="layout.flexbox.enabled",
+                    engines="gecko servo",
+                    servo_pref="layout.flexbox.enabled",
                     sub_properties="flex-grow flex-shrink flex-basis"
                     extra_prefixes="webkit"
                     derive_serialize="True"
@@ -858,7 +858,7 @@ ${helpers.four_sides_shorthand(
     "inset",
     "%s",
     "specified::LengthPercentageOrAuto::parse",
-    engines="gecko servo-2013",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-logical/#propdef-inset",
     allow_quirks="No",
 )}
@@ -868,7 +868,7 @@ ${helpers.two_properties_shorthand(
     "inset-block-start",
     "inset-block-end",
     "specified::LengthPercentageOrAuto::parse",
-    engines="gecko servo-2013",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-logical/#propdef-inset-block"
 )}
 
@@ -877,7 +877,7 @@ ${helpers.two_properties_shorthand(
     "inset-inline-start",
     "inset-inline-end",
     "specified::LengthPercentageOrAuto::parse",
-    engines="gecko servo-2013",
+    engines="gecko servo",
     spec="https://drafts.csswg.org/css-logical/#propdef-inset-inline"
 )}
 
diff --git a/servo/components/style/properties/shorthands/table.mako.rs b/servo/components/style/properties/shorthands/table.mako.rs
new file mode 100644
index 0000000000..daa3e8897c
--- /dev/null
+++ b/servo/components/style/properties/shorthands/table.mako.rs
@@ -0,0 +1,3 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
diff --git a/servo/components/style/properties/shorthands/text.mako.rs b/servo/components/style/properties/shorthands/text.mako.rs
index 5b071be2c4..a913f81875 100644
--- a/servo/components/style/properties/shorthands/text.mako.rs
+++ b/servo/components/style/properties/shorthands/text.mako.rs
@@ -5,7 +5,7 @@
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
 <%helpers:shorthand name="text-decoration"
-                    engines="gecko servo-2013 servo-2020"
+                    engines="gecko servo"
                     flags="SHORTHAND_IN_GETCS"
                     sub_properties="text-decoration-line
                     ${' text-decoration-style text-decoration-color text-decoration-thickness' if engine == 'gecko' else ''}"
diff --git a/servo/components/style/properties/shorthands/ui.mako.rs b/servo/components/style/properties/shorthands/ui.mako.rs
index 4a27d5e003..1915c65a63 100644
--- a/servo/components/style/properties/shorthands/ui.mako.rs
+++ b/servo/components/style/properties/shorthands/ui.mako.rs
@@ -18,7 +18,7 @@ macro_rules! try_parse_one {
 }
 
 <%helpers:shorthand name="transition"
-                    engines="gecko servo-2013 servo-2020"
+                    engines="gecko servo"
                     extra_prefixes="moz:layout.css.prefixes.transitions webkit"
                     sub_properties="transition-property transition-duration
                                     transition-timing-function
@@ -204,7 +204,7 @@ macro_rules! try_parse_one {
 </%helpers:shorthand>
 
 <%helpers:shorthand name="animation"
-                    engines="gecko servo-2013 servo-2020"
+                    engines="gecko servo"
                     extra_prefixes="moz:layout.css.prefixes.animations webkit"
                     sub_properties="animation-name animation-duration
                                     animation-timing-function animation-delay
@@ -295,6 +295,13 @@ macro_rules! try_parse_one {
 
     impl<'a> ToCss for LonghandsToSerialize<'a>  {
         fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result where W: fmt::Write {
+            use crate::values::specified::easing::TimingFunction;
+            use crate::values::specified::{
+                AnimationDirection, AnimationFillMode, AnimationPlayState,
+            };
+            use crate::Zero;
+            use style_traits::values::SequenceWriter;
+
             let len = self.animation_name.0.len();
             // There should be at least one declared value
             if len == 0 {
@@ -320,28 +327,83 @@ macro_rules! try_parse_one {
                     dest.write_str(", ")?;
                 }
 
-                % for name in props[2:]:
-                    self.animation_${name}.0[i].to_css(dest)?;
-                    dest.write_char(' ')?;
+                // We follow the order of this syntax:
+                // <single-animation> =
+                //   <animation-duration> ||
+                //   <easing-function> ||
+                //   <animation-delay> ||
+                //   <single-animation-iteration-count> ||
+                //   <single-animation-direction> ||
+                //   <single-animation-fill-mode> ||
+                //   <single-animation-play-state> ||
+                //   [ none | <keyframes-name> ] ||
+                //   <single-animation-timeline>
+                //
+                // https://drafts.csswg.org/css-animations-2/#animation-shorthand
+                //
+                // FIXME: Bug 1804574. The initial value of duration should be auto, per
+                // css-animations-2.
+                let has_duration = !self.animation_duration.0[i].is_zero();
+                let has_timing_function = !self.animation_timing_function.0[i].is_ease();
+                let has_delay = !self.animation_delay.0[i].is_zero();
+                let has_iteration_count = !self.animation_iteration_count.0[i].is_one();
+                let has_direction =
+                    !matches!(self.animation_direction.0[i], AnimationDirection::Normal);
+                let has_fill_mode =
+                    !matches!(self.animation_fill_mode.0[i], AnimationFillMode::None);
+                let has_play_state =
+                    !matches!(self.animation_play_state.0[i], AnimationPlayState::Running);
+                let animation_name = &self.animation_name.0[i];
+                let has_name = !animation_name.is_none();
+                let has_timeline = match self.animation_timeline {
+                    Some(timeline) => !timeline.0[i].is_auto(),
+                    _ => false,
+                };
+
+                let mut writer = SequenceWriter::new(dest, " ");
+
+                // To avoid ambiguity, we have to serialize duration if both duration is initial
+                // but delay is not. (In other words, it's ambiguous if we serialize delay only.)
+                if has_duration || has_delay {
+                    writer.item(&self.animation_duration.0[i])?;
+                }
+
+                if has_timing_function || TimingFunction::match_keywords(animation_name) {
+                    writer.item(&self.animation_timing_function.0[i])?;
+                }
+
+                // For animation-delay and animation-iteration-count.
+                % for name in props[4:6]:
+                if has_${name} {
+                    writer.item(&self.animation_${name}.0[i])?;
+                }
                 % endfor
 
-                self.animation_name.0[i].to_css(dest)?;
+                if has_direction || AnimationDirection::match_keywords(animation_name) {
+                    writer.item(&self.animation_direction.0[i])?;
+                }
+
+                if has_fill_mode || AnimationFillMode::match_keywords(animation_name) {
+                    writer.item(&self.animation_fill_mode.0[i])?;
+                }
 
-                // Based on the spec, the default values of other properties must be output in at
-                // least the cases necessary to distinguish an animation-name. The serialization
-                // order of animation-timeline is always later than animation-name, so it's fine
-                // to not serialize it if it is the default value. It's still possible to
-                // distinguish them (because we always serialize animation-name).
-                // https://drafts.csswg.org/css-animations-1/#animation
-                // https://drafts.csswg.org/css-animations-2/#typedef-single-animation
-                //
-                // Note: it's also fine to always serialize this. However, it seems Blink
-                // doesn't serialize default animation-timeline now, so we follow the same rule.
-                if let Some(ref timeline) = self.animation_timeline {
-                    if !timeline.0[i].is_auto() {
-                        dest.write_char(' ')?;
-                        timeline.0[i].to_css(dest)?;
-                    }
+                if has_play_state || AnimationPlayState::match_keywords(animation_name) {
+                    writer.item(&self.animation_play_state.0[i])?;
+                }
+
+                // If all values are initial, we must serialize animation-name.
+                let has_any = {
+                    has_timeline
+                % for name in props[2:]:
+                        || has_${name}
+                % endfor
+                };
+                if has_name || !has_any {
+                    writer.item(animation_name)?;
+                }
+
+                if has_timeline {
+                    writer.item(&self.animation_timeline.unwrap().0[i])?;
                 }
             }
             Ok(())
diff --git a/servo/components/style/properties/shorthands/xul.mako.rs b/servo/components/style/properties/shorthands/xul.mako.rs
new file mode 100644
index 0000000000..daa3e8897c
--- /dev/null
+++ b/servo/components/style/properties/shorthands/xul.mako.rs
@@ -0,0 +1,3 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
diff --git a/servo/components/style/queries/condition.rs b/servo/components/style/queries/condition.rs
index e17e6abd2e..25af4cdb01 100644
--- a/servo/components/style/queries/condition.rs
+++ b/servo/components/style/queries/condition.rs
@@ -13,6 +13,7 @@ use crate::{error_reporting::ContextualParseError, parser::ParserContext};
 use cssparser::{Parser, Token};
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+use selectors::kleene_value::KleeneValue;
 
 /// A binary `and` or `or` operator.
 #[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToCss, ToShmem)]
@@ -29,93 +30,6 @@ enum AllowOr {
     No,
 }
 
-/// https://en.wikipedia.org/wiki/Three-valued_logic#Kleene_and_Priest_logics
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToCss)]
-pub enum KleeneValue {
-    /// False
-    False = 0,
-    /// True
-    True = 1,
-    /// Either true or false, but we’re not sure which yet.
-    Unknown,
-}
-
-impl From<bool> for KleeneValue {
-    fn from(b: bool) -> Self {
-        if b {
-            Self::True
-        } else {
-            Self::False
-        }
-    }
-}
-
-impl KleeneValue {
-    /// Turns this Kleene value to a bool, taking the unknown value as an
-    /// argument.
-    pub fn to_bool(self, unknown: bool) -> bool {
-        match self {
-            Self::True => true,
-            Self::False => false,
-            Self::Unknown => unknown,
-        }
-    }
-}
-
-impl std::ops::Not for KleeneValue {
-    type Output = Self;
-
-    fn not(self) -> Self {
-        match self {
-            Self::True => Self::False,
-            Self::False => Self::True,
-            Self::Unknown => Self::Unknown,
-        }
-    }
-}
-
-// Implements the logical and operation.
-impl std::ops::BitAnd for KleeneValue {
-    type Output = Self;
-
-    fn bitand(self, other: Self) -> Self {
-        if self == Self::False || other == Self::False {
-            return Self::False;
-        }
-        if self == Self::Unknown || other == Self::Unknown {
-            return Self::Unknown;
-        }
-        Self::True
-    }
-}
-
-// Implements the logical or operation.
-impl std::ops::BitOr for KleeneValue {
-    type Output = Self;
-
-    fn bitor(self, other: Self) -> Self {
-        if self == Self::True || other == Self::True {
-            return Self::True;
-        }
-        if self == Self::Unknown || other == Self::Unknown {
-            return Self::Unknown;
-        }
-        Self::False
-    }
-}
-
-impl std::ops::BitOrAssign for KleeneValue {
-    fn bitor_assign(&mut self, other: Self) {
-        *self = *self | other;
-    }
-}
-
-impl std::ops::BitAndAssign for KleeneValue {
-    fn bitand_assign(&mut self, other: Self) {
-        *self = *self & other;
-    }
-}
-
 /// Represents a condition.
 #[derive(Clone, Debug, MallocSizeOf, PartialEq, ToShmem)]
 pub enum QueryCondition {
diff --git a/servo/components/style/queries/feature.rs b/servo/components/style/queries/feature.rs
index 83ff7e7522..2d4c60c362 100644
--- a/servo/components/style/queries/feature.rs
+++ b/servo/components/style/queries/feature.rs
@@ -4,7 +4,6 @@
 
 //! Query features.
 
-use super::condition::KleeneValue;
 use crate::parser::ParserContext;
 use crate::values::computed::{self, CSSPixelLength, Ratio, Resolution};
 use crate::values::AtomString;
@@ -12,6 +11,7 @@ use crate::Atom;
 use cssparser::Parser;
 use std::fmt;
 use style_traits::ParseError;
+use selectors::kleene_value::KleeneValue;
 
 /// A generic discriminant for an enum value.
 pub type KeywordDiscriminant = u8;
@@ -87,12 +87,12 @@ macro_rules! keyword_evaluator {
         fn __evaluate(
             context: &$crate::values::computed::Context,
             value: Option<$crate::queries::feature::KeywordDiscriminant>,
-        ) -> $crate::queries::condition::KleeneValue {
+        ) -> selectors::kleene_value::KleeneValue {
             // This unwrap is ok because the only discriminants that get
             // back to us is the ones that `parse` produces.
             let value: Option<$keyword_type> =
                 value.map(|kw| ::num_traits::cast::FromPrimitive::from_u8(kw).unwrap());
-            $crate::queries::condition::KleeneValue::from($actual_evaluator(context, value))
+                selectors::kleene_value::KleeneValue::from($actual_evaluator(context, value))
         }
 
         $crate::queries::feature::Evaluator::Enumerated {
diff --git a/servo/components/style/queries/feature_expression.rs b/servo/components/style/queries/feature_expression.rs
index c0171c2058..3450f85cba 100644
--- a/servo/components/style/queries/feature_expression.rs
+++ b/servo/components/style/queries/feature_expression.rs
@@ -8,16 +8,16 @@
 use super::feature::{Evaluator, QueryFeatureDescription};
 use super::feature::{FeatureFlags, KeywordDiscriminant};
 use crate::parser::{Parse, ParserContext};
-use crate::queries::condition::KleeneValue;
 use crate::str::{starts_with_ignore_ascii_case, string_as_ascii_lowercase};
 use crate::values::computed::{self, Ratio, ToComputedValue};
 use crate::values::specified::{Integer, Length, Number, Resolution};
 use crate::values::{AtomString, CSSFloat};
 use crate::{Atom, Zero};
 use cssparser::{Parser, Token};
-use std::cmp::{Ordering, PartialOrd};
+use std::cmp::Ordering;
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+use selectors::kleene_value::KleeneValue;
 
 /// Whether we're parsing a media or container query feature.
 #[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToShmem)]
diff --git a/servo/components/style/scoped_tls.rs b/servo/components/style/scoped_tls.rs
index 0d3267397a..6fb8730d18 100644
--- a/servo/components/style/scoped_tls.rs
+++ b/servo/components/style/scoped_tls.rs
@@ -8,7 +8,6 @@
 #![deny(missing_docs)]
 
 use crate::global_style_data::STYLO_MAX_THREADS;
-use rayon;
 use std::cell::{Ref, RefCell, RefMut};
 use std::ops::DerefMut;
 
diff --git a/servo/components/style/str.rs b/servo/components/style/str.rs
index 9badcdf413..fe598f546e 100644
--- a/servo/components/style/str.rs
+++ b/servo/components/style/str.rs
@@ -8,7 +8,6 @@
 
 use num_traits::ToPrimitive;
 use std::borrow::Cow;
-use std::convert::AsRef;
 use std::iter::{Filter, Peekable};
 use std::str::Split;
 
diff --git a/servo/components/style/style_adjuster.rs b/servo/components/style/style_adjuster.rs
index a993d79d6a..78a631ec14 100644
--- a/servo/components/style/style_adjuster.rs
+++ b/servo/components/style/style_adjuster.rs
@@ -294,11 +294,9 @@ impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
                 .add_flags(ComputedValueFlags::SELF_OR_ANCESTOR_HAS_SIZE_CONTAINER_TYPE);
         }
 
-        #[cfg(feature = "servo-layout-2013")]
-        {
-            if self.style.get_parent_column().is_multicol() {
-                self.style.add_flags(ComputedValueFlags::CAN_BE_FRAGMENTED);
-            }
+        #[cfg(feature = "servo")]
+        if self.style.get_parent_column().is_multicol() {
+            self.style.add_flags(ComputedValueFlags::CAN_BE_FRAGMENTED);
         }
     }
 
diff --git a/servo/components/style/stylesheets/container_rule.rs b/servo/components/style/stylesheets/container_rule.rs
index 28c387fde2..77dfa0e179 100644
--- a/servo/components/style/stylesheets/container_rule.rs
+++ b/servo/components/style/stylesheets/container_rule.rs
@@ -11,7 +11,6 @@ use crate::dom::TElement;
 use crate::logical_geometry::{LogicalSize, WritingMode};
 use crate::parser::ParserContext;
 use crate::properties::ComputedValues;
-use crate::queries::condition::KleeneValue;
 use crate::queries::feature::{AllowsRanges, Evaluator, FeatureFlags, QueryFeatureDescription};
 use crate::queries::values::Orientation;
 use crate::queries::{FeatureType, QueryCondition};
@@ -31,6 +30,7 @@ use malloc_size_of::{MallocSizeOfOps, MallocUnconditionalShallowSizeOf};
 use servo_arc::Arc;
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ParseError, ToCss};
+use selectors::kleene_value::KleeneValue;
 
 /// A container rule.
 #[derive(Debug, ToShmem)]
diff --git a/servo/components/style/stylesheets/import_rule.rs b/servo/components/style/stylesheets/import_rule.rs
index e96134b436..d539471590 100644
--- a/servo/components/style/stylesheets/import_rule.rs
+++ b/servo/components/style/stylesheets/import_rule.rs
@@ -20,7 +20,7 @@ use crate::values::CssUrl;
 use cssparser::{Parser, SourceLocation};
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ToCss};
-use to_shmem::{self, SharedMemoryBuilder, ToShmem};
+use to_shmem::{SharedMemoryBuilder, ToShmem};
 
 /// A sheet that is held from an import rule.
 #[cfg(feature = "gecko")]
diff --git a/servo/components/style/stylesheets/mod.rs b/servo/components/style/stylesheets/mod.rs
index 2bf75565de..6bb8e19fb4 100644
--- a/servo/components/style/stylesheets/mod.rs
+++ b/servo/components/style/stylesheets/mod.rs
@@ -23,15 +23,17 @@ mod property_rule;
 mod rule_list;
 mod rule_parser;
 mod rules_iterator;
+mod starting_style_rule;
 mod style_rule;
 mod stylesheet;
 pub mod supports_rule;
+mod scope_rule;
 
 #[cfg(feature = "gecko")]
 use crate::gecko_bindings::sugar::refptr::RefCounted;
 #[cfg(feature = "gecko")]
 use crate::gecko_bindings::{bindings, structs};
-use crate::parser::ParserContext;
+use crate::parser::{NestingContext, ParserContext};
 use crate::shared_lock::{DeepCloneParams, DeepCloneWithLock, Locked};
 use crate::shared_lock::{SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard};
 use crate::str::CssStringWriter;
@@ -45,7 +47,7 @@ use std::fmt;
 use std::mem::{self, ManuallyDrop};
 use style_traits::ParsingMode;
 #[cfg(feature = "gecko")]
-use to_shmem::{self, SharedMemoryBuilder, ToShmem};
+use to_shmem::{SharedMemoryBuilder, ToShmem};
 
 pub use self::container_rule::ContainerRule;
 pub use self::counter_style_rule::CounterStyleRule;
@@ -69,7 +71,9 @@ pub use self::rules_iterator::{AllRules, EffectiveRules};
 pub use self::rules_iterator::{
     EffectiveRulesIterator, NestedRuleIterationCondition, RulesIterator,
 };
+pub use self::starting_style_rule::StartingStyleRule;
 pub use self::style_rule::StyleRule;
+pub use self::scope_rule::ScopeRule;
 pub use self::stylesheet::{AllowImportRules, SanitizationData, SanitizationKind};
 pub use self::stylesheet::{DocumentStyleSheet, Namespaces, Stylesheet};
 pub use self::stylesheet::{StylesheetContents, StylesheetInDocument, UserAgentStylesheets};
@@ -132,7 +136,11 @@ impl Drop for UrlExtraData {
 impl ToShmem for UrlExtraData {
     fn to_shmem(&self, _builder: &mut SharedMemoryBuilder) -> to_shmem::Result<Self> {
         if self.0 & 1 == 0 {
-            let shared_extra_datas = unsafe { &structs::URLExtraData_sShared };
+            let shared_extra_datas = unsafe {
+                std::ptr::addr_of!(structs::URLExtraData_sShared)
+                    .as_ref()
+                    .unwrap()
+            };
             let self_ptr = self.as_ref() as *const _ as *mut _;
             let sheet_id = shared_extra_datas
                 .iter()
@@ -265,6 +273,8 @@ pub enum CssRule {
     Document(Arc<DocumentRule>),
     LayerBlock(Arc<LayerBlockRule>),
     LayerStatement(Arc<LayerStatementRule>),
+    Scope(Arc<ScopeRule>),
+    StartingStyle(Arc<StartingStyleRule>),
 }
 
 impl CssRule {
@@ -309,8 +319,14 @@ impl CssRule {
             CssRule::Document(ref arc) => {
                 arc.unconditional_shallow_size_of(ops) + arc.size_of(guard, ops)
             },
+            CssRule::StartingStyle(ref arc) => {
+                arc.unconditional_shallow_size_of(ops) + arc.size_of(guard, ops)
+            }
             // TODO(emilio): Add memory reporting for these rules.
             CssRule::LayerBlock(_) | CssRule::LayerStatement(_) => 0,
+            CssRule::Scope(ref rule) => {
+                rule.unconditional_shallow_size_of(ops) + rule.size_of(guard, ops)
+            }
         }
     }
 }
@@ -349,6 +365,9 @@ pub enum CssRuleType {
     FontPaletteValues = 19,
     // 20 is an arbitrary number to use for Property.
     Property = 20,
+    Scope = 21,
+    // https://drafts.csswg.org/css-transitions-2/#the-cssstartingstylerule-interface
+    StartingStyle = 22,
 }
 
 impl CssRuleType {
@@ -436,6 +455,8 @@ impl CssRule {
             CssRule::LayerBlock(_) => CssRuleType::LayerBlock,
             CssRule::LayerStatement(_) => CssRuleType::LayerStatement,
             CssRule::Container(_) => CssRuleType::Container,
+            CssRule::Scope(_) => CssRuleType::Scope,
+            CssRule::StartingStyle(_) => CssRuleType::StartingStyle,
         }
     }
 
@@ -464,7 +485,11 @@ impl CssRule {
             None,
             None,
         );
-        context.rule_types = insert_rule_context.containing_rule_types;
+        // Override the nesting context with existing data.
+        context.nesting_context = NestingContext::new(
+            insert_rule_context.containing_rule_types,
+            insert_rule_context.parse_relative_rule_type
+        );
 
         let state = if !insert_rule_context.containing_rule_types.is_empty() {
             State::Body
@@ -567,6 +592,12 @@ impl DeepCloneWithLock for CssRule {
             CssRule::LayerBlock(ref arc) => {
                 CssRule::LayerBlock(Arc::new(arc.deep_clone_with_lock(lock, guard, params)))
             },
+            CssRule::Scope(ref arc) => {
+                CssRule::Scope(Arc::new(arc.deep_clone_with_lock(lock, guard, params)))
+            },
+            CssRule::StartingStyle(ref arc) => {
+                CssRule::StartingStyle(Arc::new(arc.deep_clone_with_lock(lock, guard, params)))
+            },
         }
     }
 }
@@ -592,6 +623,8 @@ impl ToCssWithGuard for CssRule {
             CssRule::LayerBlock(ref rule) => rule.to_css(guard, dest),
             CssRule::LayerStatement(ref rule) => rule.to_css(guard, dest),
             CssRule::Container(ref rule) => rule.to_css(guard, dest),
+            CssRule::Scope(ref rule) => rule.to_css(guard, dest),
+            CssRule::StartingStyle(ref rule) => rule.to_css(guard, dest),
         }
     }
 }
diff --git a/servo/components/style/stylesheets/page_rule.rs b/servo/components/style/stylesheets/page_rule.rs
index a1618309a3..cdcfe0b8a7 100644
--- a/servo/components/style/stylesheets/page_rule.rs
+++ b/servo/components/style/stylesheets/page_rule.rs
@@ -221,7 +221,7 @@ impl Parse for PageSelector {
     ) -> Result<Self, ParseError<'i>> {
         let name = input
             .try_parse(parse_page_name)
-            .unwrap_or(AtomIdent(atom!("")));
+            .unwrap_or(AtomIdent::new(atom!("")));
         let mut pseudos = PagePseudoClasses::default();
         while let Ok(pc) = input.try_parse(PagePseudoClass::parse) {
             pseudos.push(pc);
diff --git a/servo/components/style/stylesheets/rule_list.rs b/servo/components/style/stylesheets/rule_list.rs
index 1b9f330185..9fb7629d3d 100644
--- a/servo/components/style/stylesheets/rule_list.rs
+++ b/servo/components/style/stylesheets/rule_list.rs
@@ -16,6 +16,8 @@ use malloc_size_of::{MallocShallowSizeOf, MallocSizeOfOps};
 use servo_arc::Arc;
 use std::fmt::{self, Write};
 
+use super::CssRuleType;
+
 /// A list of CSS rules.
 #[derive(Debug, ToShmem)]
 pub struct CssRules(pub Vec<CssRule>);
@@ -136,6 +138,7 @@ pub trait CssRulesHelpers {
         parent_stylesheet_contents: &StylesheetContents,
         index: usize,
         nested: CssRuleTypes,
+        parse_relative_rule_type: Option<CssRuleType>,
         loader: Option<&dyn StylesheetLoader>,
         allow_import_rules: AllowImportRules,
     ) -> Result<CssRule, RulesMutateError>;
@@ -149,6 +152,7 @@ impl CssRulesHelpers for Locked<CssRules> {
         parent_stylesheet_contents: &StylesheetContents,
         index: usize,
         containing_rule_types: CssRuleTypes,
+        parse_relative_rule_type: Option<CssRuleType>,
         loader: Option<&dyn StylesheetLoader>,
         allow_import_rules: AllowImportRules,
     ) -> Result<CssRule, RulesMutateError> {
@@ -165,6 +169,7 @@ impl CssRulesHelpers for Locked<CssRules> {
                 rule_list: &rules.0,
                 index,
                 containing_rule_types,
+                parse_relative_rule_type,
             };
 
             // Steps 3, 4, 5, 6
diff --git a/servo/components/style/stylesheets/rule_parser.rs b/servo/components/style/stylesheets/rule_parser.rs
index 742ad5d250..634f7c1af3 100644
--- a/servo/components/style/stylesheets/rule_parser.rs
+++ b/servo/components/style/stylesheets/rule_parser.rs
@@ -23,6 +23,8 @@ use crate::stylesheets::font_feature_values_rule::parse_family_name_list;
 use crate::stylesheets::import_rule::{ImportLayer, ImportRule, ImportSupportsCondition};
 use crate::stylesheets::keyframes_rule::parse_keyframe_list;
 use crate::stylesheets::layer_rule::{LayerBlockRule, LayerName, LayerStatementRule};
+use crate::stylesheets::scope_rule::{ScopeBounds, ScopeRule};
+use crate::stylesheets::starting_style_rule::StartingStyleRule;
 use crate::stylesheets::supports_rule::SupportsCondition;
 use crate::stylesheets::{
     AllowImportRules, CorsMode, CssRule, CssRuleType, CssRuleTypes, CssRules, DocumentRule,
@@ -50,6 +52,8 @@ pub struct InsertRuleContext<'a> {
     pub index: usize,
     /// The containing rule types of our ancestors.
     pub containing_rule_types: CssRuleTypes,
+    /// Rule type determining if and how we parse relative selector syntax.
+    pub parse_relative_rule_type: Option<CssRuleType>,
 }
 
 impl<'a> InsertRuleContext<'a> {
@@ -231,6 +235,10 @@ pub enum AtRulePrelude {
     Namespace(Option<Prefix>, Namespace),
     /// A @layer rule prelude.
     Layer(Vec<LayerName>),
+    /// A @scope rule prelude.
+    Scope(ScopeBounds),
+    /// A @starting-style prelude.
+    StartingStyle,
 }
 
 impl AtRulePrelude {
@@ -251,6 +259,8 @@ impl AtRulePrelude {
             Self::Margin(..) => "margin",
             Self::Namespace(..) => "namespace",
             Self::Layer(..) => "layer",
+            Self::Scope(..) => "scope",
+            Self::StartingStyle => "starting-style",
         }
     }
 }
@@ -483,18 +493,29 @@ impl NestedParseResult {
 impl<'a, 'i> NestedRuleParser<'a, 'i> {
     #[inline]
     fn in_style_rule(&self) -> bool {
-        self.context.rule_types.contains(CssRuleType::Style)
+        self.context
+            .nesting_context
+            .rule_types
+            .contains(CssRuleType::Style)
     }
 
     #[inline]
     fn in_page_rule(&self) -> bool {
-        self.context.rule_types.contains(CssRuleType::Page)
+        self.context
+            .nesting_context
+            .rule_types
+            .contains(CssRuleType::Page)
     }
 
     #[inline]
     fn in_style_or_page_rule(&self) -> bool {
         let types = CssRuleTypes::from_bits(CssRuleType::Style.bit() | CssRuleType::Page.bit());
-        self.context.rule_types.intersects(types)
+        self.context.nesting_context.rule_types.intersects(types)
+    }
+
+    #[inline]
+    fn parse_relative(&self) -> ParseRelative {
+        self.context.nesting_context.parse_relative
     }
 
     // https://drafts.csswg.org/css-nesting/#conditionals
@@ -507,7 +528,9 @@ impl<'a, 'i> NestedRuleParser<'a, 'i> {
             AtRulePrelude::Supports(..) |
             AtRulePrelude::Container(..) |
             AtRulePrelude::Document(..) |
-            AtRulePrelude::Layer(..) => true,
+            AtRulePrelude::Layer(..) |
+            AtRulePrelude::Scope(..) |
+            AtRulePrelude::StartingStyle => true,
 
             AtRulePrelude::Namespace(..) |
             AtRulePrelude::FontFace |
@@ -523,10 +546,9 @@ impl<'a, 'i> NestedRuleParser<'a, 'i> {
     }
 
     fn nest_for_rule<R>(&mut self, rule_type: CssRuleType, cb: impl FnOnce(&mut Self) -> R) -> R {
-        let old_rule_types = self.context.rule_types;
-        self.context.rule_types.insert(rule_type);
+        let old = self.context.nesting_context.save(rule_type);
         let r = cb(self);
-        self.context.rule_types = old_rule_types;
+        self.context.nesting_context.restore(old);
         r
     }
 
@@ -701,6 +723,13 @@ impl<'a, 'i> AtRuleParser<'i> for NestedRuleParser<'a, 'i> {
                 let cond = DocumentCondition::parse(&self.context, input)?;
                 AtRulePrelude::Document(cond)
             },
+            "scope" if static_prefs::pref!("layout.css.at-scope.enabled") => {
+                let bounds = ScopeBounds::parse(&self.context, input, self.in_style_rule());
+                AtRulePrelude::Scope(bounds)
+            },
+            "starting-style" if static_prefs::pref!("layout.css.starting-style-at-rules.enabled") => {
+                AtRulePrelude::StartingStyle
+            },
             _ => {
                 if static_prefs::pref!("layout.css.margin-rules.enabled") {
                     if let Some(margin_rule_type) = MarginRuleType::match_name(&name) {
@@ -862,11 +891,30 @@ impl<'a, 'i> AtRuleParser<'i> for NestedRuleParser<'a, 'i> {
                     block: Arc::new(self.shared_lock.wrap(declarations)),
                     source_location: start.source_location(),
                 }))
-            }
+            },
             AtRulePrelude::Import(..) | AtRulePrelude::Namespace(..) => {
                 // These rules don't have blocks.
                 return Err(input.new_unexpected_token_error(cssparser::Token::CurlyBracketBlock));
             },
+            AtRulePrelude::Scope(bounds) => {
+                let source_location = start.source_location();
+                CssRule::Scope(Arc::new(ScopeRule {
+                    bounds,
+                    rules: self
+                        .parse_nested(input, CssRuleType::Scope)
+                        .into_rules(self.shared_lock, source_location),
+                    source_location,
+                }))
+            },
+            AtRulePrelude::StartingStyle => {
+                let source_location = start.source_location();
+                CssRule::StartingStyle(Arc::new(StartingStyleRule {
+                    rules: self
+                        .parse_nested(input, CssRuleType::StartingStyle)
+                        .into_rules(self.shared_lock, source_location),
+                    source_location,
+                }))
+            },
         };
         self.rules.push(rule);
         Ok(())
@@ -913,12 +961,7 @@ impl<'a, 'i> QualifiedRuleParser<'i> for NestedRuleParser<'a, 'i> {
             url_data: self.context.url_data,
             for_supports_rule: false,
         };
-        let parse_relative = if self.in_style_rule() {
-            ParseRelative::ForNesting
-        } else {
-            ParseRelative::No
-        };
-        SelectorList::parse(&selector_parser, input, parse_relative)
+        SelectorList::parse(&selector_parser, input, self.parse_relative())
     }
 
     fn parse_block<'t>(
diff --git a/servo/components/style/stylesheets/rules_iterator.rs b/servo/components/style/stylesheets/rules_iterator.rs
index 76d41c8184..60f3df1ea9 100644
--- a/servo/components/style/stylesheets/rules_iterator.rs
+++ b/servo/components/style/stylesheets/rules_iterator.rs
@@ -116,6 +116,8 @@ where
                 Some(supports_rule.rules.read_with(guard).0.iter())
             },
             CssRule::LayerBlock(ref layer_rule) => Some(layer_rule.rules.read_with(guard).0.iter()),
+            CssRule::Scope(ref rule) => Some(rule.rules.read_with(guard).0.iter()),
+            CssRule::StartingStyle(ref rule) => Some(rule.rules.read_with(guard).0.iter()),
         }
     }
 }
diff --git a/servo/components/style/stylesheets/scope_rule.rs b/servo/components/style/stylesheets/scope_rule.rs
new file mode 100644
index 0000000000..6816c433a7
--- /dev/null
+++ b/servo/components/style/stylesheets/scope_rule.rs
@@ -0,0 +1,161 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! A [`@scope`][scope] rule.
+//!
+//! [scope]: https://drafts.csswg.org/css-cascade-6/#scoped-styles
+
+use crate::parser::ParserContext;
+use crate::selector_parser::{SelectorImpl, SelectorParser};
+use crate::shared_lock::{
+    DeepCloneParams, DeepCloneWithLock, Locked, SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard,
+};
+use crate::str::CssStringWriter;
+use crate::stylesheets::CssRules;
+use cssparser::{Parser, SourceLocation, ToCss};
+#[cfg(feature = "gecko")]
+use malloc_size_of::{MallocSizeOfOps, MallocUnconditionalSizeOf, MallocUnconditionalShallowSizeOf};
+use selectors::parser::{ParseRelative, SelectorList};
+use servo_arc::Arc;
+use std::fmt::{self, Write};
+use style_traits::CssWriter;
+
+/// A scoped rule.
+#[derive(Debug, ToShmem)]
+pub struct ScopeRule {
+    /// Bounds at which this rule applies.
+    pub bounds: ScopeBounds,
+    /// The nested rules inside the block.
+    pub rules: Arc<Locked<CssRules>>,
+    /// The source position where this rule was found.
+    pub source_location: SourceLocation,
+}
+
+impl DeepCloneWithLock for ScopeRule {
+    fn deep_clone_with_lock(
+        &self,
+        lock: &SharedRwLock,
+        guard: &SharedRwLockReadGuard,
+        params: &DeepCloneParams,
+    ) -> Self {
+        let rules = self.rules.read_with(guard);
+        Self {
+            bounds: self.bounds.clone(),
+            rules: Arc::new(lock.wrap(rules.deep_clone_with_lock(lock, guard, params))),
+            source_location: self.source_location.clone(),
+        }
+    }
+}
+
+impl ToCssWithGuard for ScopeRule {
+    fn to_css(&self, guard: &SharedRwLockReadGuard, dest: &mut CssStringWriter) -> fmt::Result {
+        dest.write_str("@scope")?;
+        {
+            let mut writer = CssWriter::new(dest);
+            if let Some(start) = self.bounds.start.as_ref() {
+                writer.write_str(" (")?;
+                start.to_css(&mut writer)?;
+                writer.write_char(')')?;
+            }
+            if let Some(end) = self.bounds.end.as_ref() {
+                writer.write_str(" to (")?;
+                end.to_css(&mut writer)?;
+                writer.write_char(')')?;
+            }
+        }
+        self.rules.read_with(guard).to_css_block(guard, dest)
+    }
+}
+
+impl ScopeRule {
+    /// Measure heap usage.
+    #[cfg(feature = "gecko")]
+    pub fn size_of(&self, guard: &SharedRwLockReadGuard, ops: &mut MallocSizeOfOps) -> usize {
+        self.rules.unconditional_shallow_size_of(ops) +
+            self.rules.read_with(guard).size_of(guard, ops) +
+            self.bounds.size_of(ops)
+    }
+}
+
+/// Bounds of the scope.
+#[derive(Debug, Clone, ToShmem)]
+pub struct ScopeBounds {
+    /// Start of the scope.
+    pub start: Option<SelectorList<SelectorImpl>>,
+    /// End of the scope.
+    pub end: Option<SelectorList<SelectorImpl>>,
+}
+
+impl ScopeBounds {
+    #[cfg(feature = "gecko")]
+    fn size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
+        fn bound_size_of(bound: &Option<SelectorList<SelectorImpl>>, ops: &mut MallocSizeOfOps) -> usize {
+            bound.as_ref().map(|list| list.unconditional_size_of(ops)).unwrap_or(0)
+        }
+        bound_size_of(&self.start, ops) + bound_size_of(&self.end, ops)
+    }
+}
+
+fn parse_scope<'a>(
+    context: &ParserContext,
+    input: &mut Parser<'a, '_>,
+    in_style_rule: bool,
+    for_end: bool
+) -> Option<SelectorList<SelectorImpl>> {
+    input.try_parse(|input| {
+        if for_end {
+            input.expect_ident_matching("to")?;
+        }
+        input.expect_parenthesis_block()?;
+        input.parse_nested_block(|input| {
+            if input.is_exhausted() {
+                return Ok(None);
+            }
+            let selector_parser = SelectorParser {
+                stylesheet_origin: context.stylesheet_origin,
+                namespaces: &context.namespaces,
+                url_data: context.url_data,
+                for_supports_rule: false,
+            };
+            let parse_relative = if for_end {
+                ParseRelative::ForScope
+            } else if in_style_rule {
+                ParseRelative::ForNesting
+            } else {
+                ParseRelative::No
+            };
+            Ok(Some(SelectorList::parse_forgiving(
+                &selector_parser,
+                input,
+                parse_relative,
+            )?))
+        })
+    })
+    .ok()
+    .flatten()
+}
+
+impl ScopeBounds {
+    /// Parse a container condition.
+    pub fn parse<'a>(
+        context: &ParserContext,
+        input: &mut Parser<'a, '_>,
+        in_style_rule: bool,
+    ) -> Self {
+        let start = parse_scope(
+            context,
+            input,
+            in_style_rule,
+            false
+        );
+
+        let end = parse_scope(
+            context,
+            input,
+            in_style_rule,
+            true
+        );
+        Self { start, end }
+    }
+}
diff --git a/servo/components/style/stylesheets/starting_style_rule.rs b/servo/components/style/stylesheets/starting_style_rule.rs
new file mode 100644
index 0000000000..3c2627582b
--- /dev/null
+++ b/servo/components/style/stylesheets/starting_style_rule.rs
@@ -0,0 +1,57 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! before-change style: the `@starting-style` rules.
+//! https://drafts.csswg.org/css-transitions-2/#defining-before-change-style
+
+use crate::shared_lock::{DeepCloneParams, DeepCloneWithLock, Locked};
+use crate::shared_lock::{SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard};
+use crate::str::CssStringWriter;
+use crate::stylesheets::CssRules;
+use cssparser::SourceLocation;
+use malloc_size_of::{MallocSizeOfOps, MallocUnconditionalShallowSizeOf};
+use servo_arc::Arc;
+use std::fmt::{self, Debug, Write};
+
+/// A [`@starting-style`][starting-style] rule.
+///
+/// [starting-style]: https://drafts.csswg.org/css-transitions-2/#at-ruledef-starting-style
+#[derive(Debug, ToShmem)]
+pub struct StartingStyleRule {
+    /// The nested rules to this starting-style rule.
+    pub rules: Arc<Locked<CssRules>>,
+    /// The source position where this starting-style rule was found.
+    pub source_location: SourceLocation,
+}
+
+impl StartingStyleRule {
+    /// Measure heap usage.
+    #[cfg(feature = "gecko")]
+    pub fn size_of(&self, guard: &SharedRwLockReadGuard, ops: &mut MallocSizeOfOps) -> usize {
+        self.rules.unconditional_shallow_size_of(ops) +
+            self.rules.read_with(guard).size_of(guard, ops)
+    }
+}
+
+impl ToCssWithGuard for StartingStyleRule {
+    fn to_css(&self, guard: &SharedRwLockReadGuard, dest: &mut CssStringWriter) -> fmt::Result {
+        dest.write_str("@starting-style")?;
+        self.rules.read_with(guard).to_css_block(guard, dest)
+    }
+}
+
+impl DeepCloneWithLock for StartingStyleRule {
+    fn deep_clone_with_lock(
+        &self,
+        lock: &SharedRwLock,
+        guard: &SharedRwLockReadGuard,
+        params: &DeepCloneParams,
+    ) -> Self {
+        let rules = self.rules.read_with(guard);
+        StartingStyleRule {
+            rules: Arc::new(lock.wrap(rules.deep_clone_with_lock(lock, guard, params))),
+            source_location: self.source_location.clone(),
+        }
+    }
+}
diff --git a/servo/components/style/stylesheets/stylesheet.rs b/servo/components/style/stylesheets/stylesheet.rs
index 1604022871..84d84b0d46 100644
--- a/servo/components/style/stylesheets/stylesheet.rs
+++ b/servo/components/style/stylesheets/stylesheet.rs
@@ -333,7 +333,11 @@ impl SanitizationKind {
             // TODO(emilio): Perhaps Layer should not be always sanitized? But
             // we sanitize @media and co, so this seems safer for now.
             CssRule::LayerStatement(..) |
-            CssRule::LayerBlock(..) => false,
+            CssRule::LayerBlock(..) |
+            // TODO(dshin): Same comment as Layer applies - shouldn't give away
+            // something like display size - erring on the side of "safe" for now.
+            CssRule::Scope(..) |
+            CssRule::StartingStyle(..) => false,
 
             CssRule::FontFace(..) | CssRule::Namespace(..) | CssRule::Style(..) => true,
 
diff --git a/servo/components/style/stylist.rs b/servo/components/style/stylist.rs
index cc1cb75689..06cbe6276b 100644
--- a/servo/components/style/stylist.rs
+++ b/servo/components/style/stylist.rs
@@ -31,7 +31,7 @@ use crate::rule_collector::RuleCollector;
 use crate::rule_tree::{CascadeLevel, RuleTree, StrongRuleNode, StyleSource};
 use crate::sharing::RevalidationResult;
 use crate::selector_map::{PrecomputedHashMap, PrecomputedHashSet, SelectorMap, SelectorMapEntry};
-use crate::selector_parser::{PerPseudoElementMap, PseudoElement, SelectorImpl, SnapshotMap};
+use crate::selector_parser::{PerPseudoElementMap, PseudoElement, SelectorImpl, NonTSPseudoClass, SnapshotMap};
 use crate::shared_lock::{Locked, SharedRwLockReadGuard, StylesheetGuards};
 use crate::stylesheet_set::{DataValidity, DocumentStylesheetSet, SheetRebuildKind};
 use crate::stylesheet_set::{DocumentStylesheetFlusher, SheetCollectionFlusher};
@@ -48,7 +48,7 @@ use crate::stylesheets::{
     PerOriginIter,
 };
 use crate::stylesheets::{StyleRule, StylesheetContents, StylesheetInDocument};
-use crate::values::computed;
+use crate::values::{computed, AtomIdent};
 use crate::AllocErr;
 use crate::{Atom, LocalName, Namespace, ShrinkIfNeeded, WeakAtom};
 use dom::{DocumentState, ElementState};
@@ -113,8 +113,6 @@ unsafe impl Send for CascadeDataCacheKey {}
 unsafe impl Sync for CascadeDataCacheKey {}
 
 trait CascadeDataCacheEntry: Sized {
-    /// Returns a reference to the cascade data.
-    fn cascade_data(&self) -> &CascadeData;
     /// Rebuilds the cascade data for the new stylesheet collection. The
     /// collection is guaranteed to be dirty.
     fn rebuild<S>(
@@ -269,10 +267,6 @@ lazy_static! {
 }
 
 impl CascadeDataCacheEntry for UserAgentCascadeData {
-    fn cascade_data(&self) -> &CascadeData {
-        &self.cascade_data
-    }
-
     fn rebuild<S>(
         device: &Device,
         quirks_mode: QuirksMode,
@@ -2023,6 +2017,11 @@ struct StylistSelectorVisitor<'a> {
     /// selectors.
     nth_of_attribute_dependencies: &'a mut PrecomputedHashSet<LocalName>,
 
+    /// The filter with the local names of custom states in selectors for
+    /// within the selector list of :nth-child(... of <selector list>)
+    /// selectors.
+    nth_of_custom_state_dependencies: &'a mut PrecomputedHashSet<AtomIdent>,
+
     /// All the states selectors in the page reference.
     state_dependencies: &'a mut ElementState,
 
@@ -2144,6 +2143,16 @@ impl<'a> SelectorVisitor for StylistSelectorVisitor<'a> {
             component_needs_revalidation(s, self.passed_rightmost_selector);
 
         match *s {
+            Component::NonTSPseudoClass(NonTSPseudoClass::CustomState(ref name)) => {
+                // CustomStateSet is special cased as it is a functional pseudo
+                // class with unbounded inner values. This is different to
+                // other psuedo class like :emtpy or :dir() which can be packed
+                // into the ElementState bitflags. For CustomState, however,
+                // the state name should be checked for presence in the selector.
+                if self.in_selector_list_of.relevant_to_nth_of_dependencies() {
+                    self.nth_of_custom_state_dependencies.insert(name.0.clone());
+                }
+            },
             Component::NonTSPseudoClass(ref p) => {
                 self.state_dependencies.insert(p.state_flag());
                 self.document_state_dependencies
@@ -2377,6 +2386,11 @@ pub struct CascadeData {
     /// an element when an irrelevant attribute changes.
     nth_of_attribute_dependencies: PrecomputedHashSet<LocalName>,
 
+    /// The custom states that appear in the selector list of
+    /// :nth-child(... of <selector list>). Used to avoid restyling siblings of
+    /// an element when an irrelevant custom state changes.
+    nth_of_custom_state_dependencies: PrecomputedHashSet<AtomIdent>,
+
     /// The element state bits that are relied on by selectors.  Like
     /// `attribute_dependencies`, this is used to avoid taking element snapshots
     /// when an irrelevant element state bit changes.
@@ -2456,6 +2470,7 @@ impl CascadeData {
             nth_of_mapped_ids: PrecomputedHashSet::default(),
             nth_of_class_dependencies: PrecomputedHashSet::default(),
             nth_of_attribute_dependencies: PrecomputedHashSet::default(),
+            nth_of_custom_state_dependencies: PrecomputedHashSet::default(),
             nth_of_state_dependencies: ElementState::empty(),
             attribute_dependencies: PrecomputedHashSet::default(),
             state_dependencies: ElementState::empty(),
@@ -2535,6 +2550,13 @@ impl CascadeData {
         self.state_dependencies.intersects(state)
     }
 
+    /// Returns whether the given Custom State is relied upon by a selector
+    /// of some rule in the selector list of :nth-child(... of <selector list>).
+    #[inline]
+    pub fn has_nth_of_custom_state_dependency(&self, state: &AtomIdent) -> bool {
+        self.nth_of_custom_state_dependencies.contains(state)
+    }
+
     /// Returns whether the given ElementState bit is relied upon by a selector
     /// of some rule in the selector list of :nth-child(... of <selector list>).
     #[inline]
@@ -2664,6 +2686,7 @@ impl CascadeData {
         self.relative_selector_invalidation_map.shrink_if_needed();
         self.attribute_dependencies.shrink_if_needed();
         self.nth_of_attribute_dependencies.shrink_if_needed();
+        self.nth_of_custom_state_dependencies.shrink_if_needed();
         self.nth_of_class_dependencies.shrink_if_needed();
         self.nth_of_mapped_ids.shrink_if_needed();
         self.mapped_ids.shrink_if_needed();
@@ -2859,6 +2882,8 @@ impl CascadeData {
                                 nth_of_class_dependencies: &mut self.nth_of_class_dependencies,
                                 nth_of_attribute_dependencies: &mut self
                                     .nth_of_attribute_dependencies,
+                                nth_of_custom_state_dependencies: &mut self
+                                    .nth_of_custom_state_dependencies,
                                 state_dependencies: &mut self.state_dependencies,
                                 nth_of_state_dependencies: &mut self.nth_of_state_dependencies,
                                 document_state_dependencies: &mut self.document_state_dependencies,
@@ -3234,7 +3259,9 @@ impl CascadeData {
                 CssRule::LayerBlock(..) |
                 CssRule::LayerStatement(..) |
                 CssRule::FontPaletteValues(..) |
-                CssRule::FontFeatureValues(..) => {
+                CssRule::FontFeatureValues(..) |
+                CssRule::Scope(..) |
+                CssRule::StartingStyle(..) => {
                     // Not affected by device changes.
                     continue;
                 },
@@ -3323,6 +3350,7 @@ impl CascadeData {
         self.relative_selector_invalidation_map.clear();
         self.attribute_dependencies.clear();
         self.nth_of_attribute_dependencies.clear();
+        self.nth_of_custom_state_dependencies.clear();
         self.nth_of_class_dependencies.clear();
         self.state_dependencies = ElementState::empty();
         self.nth_of_state_dependencies = ElementState::empty();
@@ -3335,10 +3363,6 @@ impl CascadeData {
 }
 
 impl CascadeDataCacheEntry for CascadeData {
-    fn cascade_data(&self) -> &CascadeData {
-        self
-    }
-
     fn rebuild<S>(
         device: &Device,
         quirks_mode: QuirksMode,
@@ -3482,6 +3506,7 @@ pub fn needs_revalidation_for_testing(s: &Selector<SelectorImpl>) -> bool {
     let mut attribute_dependencies = Default::default();
     let mut nth_of_class_dependencies = Default::default();
     let mut nth_of_attribute_dependencies = Default::default();
+    let mut nth_of_custom_state_dependencies = Default::default();
     let mut state_dependencies = ElementState::empty();
     let mut nth_of_state_dependencies = ElementState::empty();
     let mut document_state_dependencies = DocumentState::empty();
@@ -3494,6 +3519,7 @@ pub fn needs_revalidation_for_testing(s: &Selector<SelectorImpl>) -> bool {
         attribute_dependencies: &mut attribute_dependencies,
         nth_of_class_dependencies: &mut nth_of_class_dependencies,
         nth_of_attribute_dependencies: &mut nth_of_attribute_dependencies,
+        nth_of_custom_state_dependencies: &mut nth_of_custom_state_dependencies,
         state_dependencies: &mut state_dependencies,
         nth_of_state_dependencies: &mut nth_of_state_dependencies,
         document_state_dependencies: &mut document_state_dependencies,
diff --git a/servo/components/style/traversal.rs b/servo/components/style/traversal.rs
index d63c3cb965..fa256d0f60 100644
--- a/servo/components/style/traversal.rs
+++ b/servo/components/style/traversal.rs
@@ -688,7 +688,7 @@ where
     element.finish_restyle(context, data, new_styles, important_rules_changed)
 }
 
-#[cfg(feature = "servo-layout-2013")]
+#[cfg(feature = "servo")]
 fn notify_paint_worklet<E>(context: &StyleContext<E>, data: &ElementData)
 where
     E: TElement,
@@ -726,7 +726,7 @@ where
     }
 }
 
-#[cfg(not(feature = "servo-layout-2013"))]
+#[cfg(not(feature = "servo"))]
 fn notify_paint_worklet<E>(_context: &StyleContext<E>, _data: &ElementData)
 where
     E: TElement,
diff --git a/servo/components/style/values/computed/basic_shape.rs b/servo/components/style/values/computed/basic_shape.rs
index d39110ec1c..21df7baf93 100644
--- a/servo/components/style/values/computed/basic_shape.rs
+++ b/servo/components/style/values/computed/basic_shape.rs
@@ -7,9 +7,12 @@
 //!
 //! [basic-shape]: https://drafts.csswg.org/css-shapes/#typedef-basic-shape
 
+use crate::values::animated::{Animate, Procedure};
+use crate::values::computed::angle::Angle;
 use crate::values::computed::url::ComputedUrl;
 use crate::values::computed::{Image, LengthPercentage, NonNegativeLengthPercentage, Position};
 use crate::values::generics::basic_shape as generic;
+use crate::values::specified::svg_path::{CoordPair, PathCommand};
 
 /// A computed alias for FillRule.
 pub use crate::values::generics::basic_shape::FillRule;
@@ -21,8 +24,13 @@ pub type ClipPath = generic::GenericClipPath<BasicShape, ComputedUrl>;
 pub type ShapeOutside = generic::GenericShapeOutside<BasicShape, Image>;
 
 /// A computed basic shape.
-pub type BasicShape =
-    generic::GenericBasicShape<Position, LengthPercentage, NonNegativeLengthPercentage, InsetRect>;
+pub type BasicShape = generic::GenericBasicShape<
+    Angle,
+    Position,
+    LengthPercentage,
+    NonNegativeLengthPercentage,
+    InsetRect,
+>;
 
 /// The computed value of `inset()`.
 pub type InsetRect = generic::GenericInsetRect<LengthPercentage, NonNegativeLengthPercentage>;
@@ -35,3 +43,179 @@ pub type Ellipse = generic::Ellipse<Position, NonNegativeLengthPercentage>;
 
 /// The computed value of `ShapeRadius`.
 pub type ShapeRadius = generic::GenericShapeRadius<NonNegativeLengthPercentage>;
+
+/// The computed value of `shape()`.
+pub type Shape = generic::Shape<Angle, LengthPercentage>;
+
+/// The computed value of `ShapeCommand`.
+pub type ShapeCommand = generic::GenericShapeCommand<Angle, LengthPercentage>;
+
+/// The computed value of `PathOrShapeFunction`.
+pub type PathOrShapeFunction = generic::GenericPathOrShapeFunction<Angle, LengthPercentage>;
+
+/// The computed value of `CoordinatePair`.
+pub type CoordinatePair = generic::CoordinatePair<LengthPercentage>;
+
+/// Animate from `Shape` to `Path`, and vice versa.
+macro_rules! animate_shape {
+    (
+        $from:ident,
+        $to:ident,
+        $procedure:ident,
+        $from_as_shape:tt,
+        $to_as_shape:tt
+    ) => {{
+        // Check fill-rule.
+        if $from.fill != $to.fill {
+            return Err(());
+        }
+
+        // Check the list of commands. (This is a specialized lists::by_computed_value::animate().)
+        let from_cmds = $from.commands();
+        let to_cmds = $to.commands();
+        if from_cmds.len() != to_cmds.len() {
+            return Err(());
+        }
+        let commands = from_cmds
+            .iter()
+            .zip(to_cmds.iter())
+            .map(|(from_cmd, to_cmd)| {
+                $from_as_shape(from_cmd).animate(&$to_as_shape(to_cmd), $procedure)
+            })
+            .collect::<Result<Vec<ShapeCommand>, ()>>()?;
+
+        Ok(Shape {
+            fill: $from.fill,
+            commands: commands.into(),
+        })
+    }};
+}
+
+impl Animate for PathOrShapeFunction {
+    #[inline]
+    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
+        // Per spec, commands are "the same" if they use the same command keyword, and use the same
+        // <by-to> keyword. For curve and smooth, they also must have the same number of control
+        // points. Therefore, we don't have to do normalization here. (Note that we do
+        // normalization if we animate from path() to path(). See svg_path.rs for more details.)
+        //
+        // https://drafts.csswg.org/css-shapes-2/#interpolating-shape
+        match (self, other) {
+            (Self::Path(ref from), Self::Path(ref to)) => {
+                from.animate(to, procedure).map(Self::Path)
+            },
+            (Self::Shape(ref from), Self::Shape(ref to)) => {
+                from.animate(to, procedure).map(Self::Shape)
+            },
+            (Self::Shape(ref from), Self::Path(ref to)) => {
+                // Animate from shape() to path(). We convert each PathCommand into ShapeCommand,
+                // and return shape().
+                animate_shape!(
+                    from,
+                    to,
+                    procedure,
+                    (|shape_cmd| shape_cmd),
+                    (|path_cmd| ShapeCommand::from(path_cmd))
+                )
+                .map(Self::Shape)
+            },
+            (Self::Path(ref from), Self::Shape(ref to)) => {
+                // Animate from path() to shape(). We convert each PathCommand into ShapeCommand,
+                // and return shape().
+                animate_shape!(
+                    from,
+                    to,
+                    procedure,
+                    (|path_cmd| ShapeCommand::from(path_cmd)),
+                    (|shape_cmd| shape_cmd)
+                )
+                .map(Self::Shape)
+            },
+        }
+    }
+}
+
+impl From<&PathCommand> for ShapeCommand {
+    #[inline]
+    fn from(path: &PathCommand) -> Self {
+        use crate::values::computed::CSSPixelLength;
+        match path {
+            &PathCommand::Close => Self::Close,
+            &PathCommand::Move { by_to, ref point } => Self::Move {
+                by_to,
+                point: point.into(),
+            },
+            &PathCommand::Line { by_to, ref point } => Self::Move {
+                by_to,
+                point: point.into(),
+            },
+            &PathCommand::HLine { by_to, x } => Self::HLine {
+                by_to,
+                x: LengthPercentage::new_length(CSSPixelLength::new(x)),
+            },
+            &PathCommand::VLine { by_to, y } => Self::VLine {
+                by_to,
+                y: LengthPercentage::new_length(CSSPixelLength::new(y)),
+            },
+            &PathCommand::CubicCurve {
+                by_to,
+                ref point,
+                ref control1,
+                ref control2,
+            } => Self::CubicCurve {
+                by_to,
+                point: point.into(),
+                control1: control1.into(),
+                control2: control2.into(),
+            },
+            &PathCommand::QuadCurve {
+                by_to,
+                ref point,
+                ref control1,
+            } => Self::QuadCurve {
+                by_to,
+                point: point.into(),
+                control1: control1.into(),
+            },
+            &PathCommand::SmoothCubic {
+                by_to,
+                ref point,
+                ref control2,
+            } => Self::SmoothCubic {
+                by_to,
+                point: point.into(),
+                control2: control2.into(),
+            },
+            &PathCommand::SmoothQuad { by_to, ref point } => Self::SmoothQuad {
+                by_to,
+                point: point.into(),
+            },
+            &PathCommand::Arc {
+                by_to,
+                ref point,
+                ref radii,
+                arc_sweep,
+                arc_size,
+                rotate,
+            } => Self::Arc {
+                by_to,
+                point: point.into(),
+                radii: radii.into(),
+                arc_sweep,
+                arc_size,
+                rotate: Angle::from_degrees(rotate),
+            },
+        }
+    }
+}
+
+impl From<&CoordPair> for CoordinatePair {
+    #[inline]
+    fn from(p: &CoordPair) -> Self {
+        use crate::values::computed::CSSPixelLength;
+        Self::new(
+            LengthPercentage::new_length(CSSPixelLength::new(p.x)),
+            LengthPercentage::new_length(CSSPixelLength::new(p.y)),
+        )
+    }
+}
diff --git a/servo/components/style/values/computed/box.rs b/servo/components/style/values/computed/box.rs
index 62811d9851..0dea1c7ab9 100644
--- a/servo/components/style/values/computed/box.rs
+++ b/servo/components/style/values/computed/box.rs
@@ -383,6 +383,15 @@ impl Zoom {
         if self == Self::ONE {
             return value;
         }
-        self.value() * value
+        value * self.value()
+    }
+
+    /// Returns the un-zoomed value.
+    #[inline]
+    pub fn unzoom(self, value: f32) -> f32 {
+        if self == Self::ONE {
+            return value;
+        }
+        value / self.value()
     }
 }
diff --git a/servo/components/style/values/computed/font.rs b/servo/components/style/values/computed/font.rs
index de0a5e372b..e492584f75 100644
--- a/servo/components/style/values/computed/font.rs
+++ b/servo/components/style/values/computed/font.rs
@@ -8,7 +8,7 @@ use crate::parser::{Parse, ParserContext};
 use crate::values::animated::ToAnimatedValue;
 use crate::values::computed::{
     Angle, Context, Integer, Length, NonNegativeLength, NonNegativeNumber, Number, Percentage,
-    ToComputedValue,
+    ToComputedValue, Zoom,
 };
 use crate::values::generics::font::{
     FeatureTagValue, FontSettings, TaggedFontValue, VariationValue,
@@ -278,6 +278,16 @@ impl FontSize {
         self.used_size.0
     }
 
+    /// Apply zoom to the font-size. This is usually done by ToComputedValue.
+    #[inline]
+    pub fn zoom(&self, zoom: Zoom) -> Self {
+        Self {
+            computed_size: NonNegative(Length::new(zoom.zoom(self.computed_size.0.px()))),
+            used_size: NonNegative(Length::new(zoom.zoom(self.used_size.0.px()))),
+            keyword_info: self.keyword_info,
+        }
+    }
+
     #[inline]
     /// Get default value of font size.
     pub fn medium() -> Self {
@@ -1359,7 +1369,7 @@ impl ToResolvedValue for LineHeight {
             context.style.get_font(),
             wm,
             Some(context.element_info.element),
-        ))
+        ).to_resolved_value(context))
     }
 
     #[inline]
diff --git a/servo/components/style/values/computed/length.rs b/servo/components/style/values/computed/length.rs
index e75676a76d..881efed126 100644
--- a/servo/components/style/values/computed/length.rs
+++ b/servo/components/style/values/computed/length.rs
@@ -6,12 +6,13 @@
 
 use super::{Context, Number, ToComputedValue};
 use crate::values::animated::ToAnimatedValue;
-use crate::values::computed::NonNegativeNumber;
+use crate::values::computed::{NonNegativeNumber, Zoom};
 use crate::values::generics::length as generics;
 use crate::values::generics::length::{
     GenericLengthOrNumber, GenericLengthPercentageOrNormal, GenericMaxSize, GenericSize,
 };
 use crate::values::generics::NonNegative;
+use crate::values::resolved::{Context as ResolvedContext, ToResolvedValue};
 use crate::values::specified::length::{AbsoluteLength, FontBaseSize, LineHeightBase};
 use crate::values::{specified, CSSFloat};
 use crate::Zero;
@@ -227,12 +228,24 @@ impl Size {
     ToAnimatedValue,
     ToAnimatedZero,
     ToComputedValue,
-    ToResolvedValue,
     ToShmem,
 )]
 #[repr(C)]
 pub struct CSSPixelLength(CSSFloat);
 
+impl ToResolvedValue for CSSPixelLength {
+    type ResolvedValue = Self;
+
+    fn to_resolved_value(self, context: &ResolvedContext) -> Self::ResolvedValue {
+        Self(context.style.effective_zoom.unzoom(self.0))
+    }
+
+    #[inline]
+    fn from_resolved_value(value: Self::ResolvedValue) -> Self {
+        value
+    }
+}
+
 impl fmt::Debug for CSSPixelLength {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         self.0.fmt(f)?;
@@ -271,6 +284,12 @@ impl CSSPixelLength {
         self.0
     }
 
+    /// Zooms a particular length.
+    #[inline]
+    pub fn zoom(self, zoom: Zoom) -> Self {
+        Self::new(zoom.zoom(self.px()))
+    }
+
     /// Return the length with app_unit i32 type.
     #[inline]
     pub fn to_i32_au(self) -> i32 {
diff --git a/servo/components/style/values/computed/length_percentage.rs b/servo/components/style/values/computed/length_percentage.rs
index 0dbd2de76d..c448025dd1 100644
--- a/servo/components/style/values/computed/length_percentage.rs
+++ b/servo/components/style/values/computed/length_percentage.rs
@@ -30,6 +30,7 @@ use crate::values::animated::{Animate, Procedure, ToAnimatedValue, ToAnimatedZer
 use crate::values::distance::{ComputeSquaredDistance, SquaredDistance};
 use crate::values::generics::calc::{CalcUnits, PositivePercentageBasis};
 use crate::values::generics::{calc, NonNegative};
+use crate::values::resolved::{Context as ResolvedContext, ToResolvedValue};
 use crate::values::specified::length::{FontBaseSize, LineHeightBase};
 use crate::values::{specified, CSSFloat};
 use crate::{Zero, ZeroNoPercent};
@@ -164,6 +165,25 @@ impl MallocSizeOf for LengthPercentage {
     }
 }
 
+impl ToResolvedValue for LengthPercentage {
+    type ResolvedValue = Self;
+
+    fn to_resolved_value(self, context: &ResolvedContext) -> Self::ResolvedValue {
+        if context.style.effective_zoom.is_one() {
+            return self;
+        }
+        match self.unpack() {
+            Unpacked::Length(l) => Self::new_length(l.to_resolved_value(context)),
+            Unpacked::Percentage(..) | Unpacked::Calc(..) => self,
+        }
+    }
+
+    #[inline]
+    fn from_resolved_value(value: Self::ResolvedValue) -> Self {
+        value
+    }
+}
+
 /// An unpacked `<length-percentage>` that borrows the `calc()` variant.
 #[derive(Clone, Debug, PartialEq, ToCss)]
 enum Unpacked<'a> {
diff --git a/servo/components/style/values/computed/ratio.rs b/servo/components/style/values/computed/ratio.rs
index ae8997cfc0..6964eec3e4 100644
--- a/servo/components/style/values/computed/ratio.rs
+++ b/servo/components/style/values/computed/ratio.rs
@@ -9,7 +9,7 @@ use crate::values::computed::NonNegativeNumber;
 use crate::values::distance::{ComputeSquaredDistance, SquaredDistance};
 use crate::values::generics::ratio::Ratio as GenericRatio;
 use crate::{One, Zero};
-use std::cmp::{Ordering, PartialOrd};
+use std::cmp::Ordering;
 
 /// A computed <ratio> value.
 pub type Ratio = GenericRatio<NonNegativeNumber>;
diff --git a/servo/components/style/values/generics/basic_shape.rs b/servo/components/style/values/generics/basic_shape.rs
index 13d27995c1..ca7646fb13 100644
--- a/servo/components/style/values/generics/basic_shape.rs
+++ b/servo/components/style/values/generics/basic_shape.rs
@@ -10,7 +10,7 @@ use crate::values::distance::{ComputeSquaredDistance, SquaredDistance};
 use crate::values::generics::border::GenericBorderRadius;
 use crate::values::generics::position::GenericPositionOrAuto;
 use crate::values::generics::rect::Rect;
-use crate::values::specified::SVGPathData;
+use crate::values::specified::svg_path::{PathCommand, SVGPathData};
 use crate::Zero;
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ToCss};
@@ -181,8 +181,13 @@ pub use self::GenericShapeOutside as ShapeOutside;
     ToShmem,
 )]
 #[repr(C, u8)]
-pub enum GenericBasicShape<Position, LengthPercentage, NonNegativeLengthPercentage, BasicShapeRect>
-{
+pub enum GenericBasicShape<
+    Angle,
+    Position,
+    LengthPercentage,
+    NonNegativeLengthPercentage,
+    BasicShapeRect,
+> {
     /// The <basic-shape-rect>.
     Rect(BasicShapeRect),
     /// Defines a circle with a center and a radius.
@@ -199,10 +204,11 @@ pub enum GenericBasicShape<Position, LengthPercentage, NonNegativeLengthPercenta
     ),
     /// Defines a polygon with pair arguments.
     Polygon(GenericPolygon<LengthPercentage>),
-    /// Defines a path with SVG path syntax.
-    Path(Path),
-    // TODO: Bug 1823463. Add shape().
-    // https://drafts.csswg.org/css-shapes-2/#shape-function
+    /// Defines a path() or shape().
+    PathOrShape(
+        #[animation(field_bound)]
+        #[css(field_bound)]
+        GenericPathOrShapeFunction<Angle, LengthPercentage>),
 }
 
 pub use self::GenericBasicShape as BasicShape;
@@ -366,6 +372,30 @@ pub use self::GenericPolygon as Polygon;
 #[repr(C)]
 pub struct PolygonCoord<LengthPercentage>(pub LengthPercentage, pub LengthPercentage);
 
+/// path() function or shape() function.
+#[derive(
+    Clone,
+    ComputeSquaredDistance,
+    Debug,
+    Deserialize,
+    MallocSizeOf,
+    PartialEq,
+    Serialize,
+    SpecifiedValueInfo,
+    ToAnimatedValue,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C, u8)]
+pub enum GenericPathOrShapeFunction<Angle, LengthPercentage> {
+    /// Defines a path with SVG path syntax.
+    Path(Path),
+    /// Defines a shape function, which is identical to path() but it uses the CSS syntax.
+    Shape(#[css(field_bound)] Shape<Angle, LengthPercentage>),
+}
+
 // https://drafts.csswg.org/css-shapes/#typedef-fill-rule
 // NOTE: Basic shapes spec says that these are the only two values, however
 // https://www.w3.org/TR/SVG/painting.html#FillRuleProperty
@@ -397,9 +427,9 @@ pub enum FillRule {
     Evenodd,
 }
 
-/// The path function defined in css-shape-2.
+/// The path function.
 ///
-/// https://drafts.csswg.org/css-shapes-2/#funcdef-path
+/// https://drafts.csswg.org/css-shapes-1/#funcdef-basic-shape-path
 #[derive(
     Animate,
     Clone,
@@ -426,6 +456,14 @@ pub struct Path {
     pub path: SVGPathData,
 }
 
+impl Path {
+    /// Returns the slice of PathCommand.
+    #[inline]
+    pub fn commands(&self) -> &[PathCommand] {
+        self.path.commands()
+    }
+}
+
 impl<B, U> ToAnimatedZero for ClipPath<B, U> {
     fn to_animated_zero(&self) -> Result<Self, ()> {
         Err(())
@@ -565,3 +603,479 @@ impl Default for FillRule {
 fn is_default<T: Default + PartialEq>(fill: &T) -> bool {
     *fill == Default::default()
 }
+
+/// The shape function defined in css-shape-2.
+/// shape() = shape(<fill-rule>? from <coordinate-pair>, <shape-command>#)
+///
+/// https://drafts.csswg.org/css-shapes-2/#shape-function
+#[derive(
+    Clone,
+    Debug,
+    Deserialize,
+    MallocSizeOf,
+    PartialEq,
+    Serialize,
+    SpecifiedValueInfo,
+    ToAnimatedValue,
+    ToComputedValue,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C)]
+pub struct Shape<Angle, LengthPercentage> {
+    /// The filling rule for this shape.
+    pub fill: FillRule,
+    /// The shape command data. Note that the starting point will be the first command in this
+    /// slice.
+    // Note: The first command is always GenericShapeCommand::Move.
+    pub commands: crate::OwnedSlice<GenericShapeCommand<Angle, LengthPercentage>>,
+}
+
+impl<Angle, LengthPercentage> Shape<Angle, LengthPercentage> {
+    /// Returns the slice of GenericShapeCommand<..>.
+    #[inline]
+    pub fn commands(&self) -> &[GenericShapeCommand<Angle, LengthPercentage>] {
+        &self.commands
+    }
+}
+
+impl<Angle, LengthPercentage> Animate for Shape<Angle, LengthPercentage>
+where
+    Angle: Animate,
+    LengthPercentage: Animate,
+{
+    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
+        if self.fill != other.fill {
+            return Err(());
+        }
+        let commands =
+            lists::by_computed_value::animate(&self.commands, &other.commands, procedure)?;
+        Ok(Self {
+            fill: self.fill,
+            commands,
+        })
+    }
+}
+
+impl<Angle, LengthPercentage> ComputeSquaredDistance for Shape<Angle, LengthPercentage>
+where
+    Angle: ComputeSquaredDistance,
+    LengthPercentage: ComputeSquaredDistance,
+{
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        if self.fill != other.fill {
+            return Err(());
+        }
+        lists::by_computed_value::squared_distance(&self.commands, &other.commands)
+    }
+}
+
+impl<Angle, LengthPercentage> ToCss for Shape<Angle, LengthPercentage>
+where
+    Angle: ToCss + Zero,
+    LengthPercentage: PartialEq + ToCss,
+{
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        use style_traits::values::SequenceWriter;
+
+        // Per spec, we must have the first move command and at least one following command.
+        debug_assert!(self.commands.len() > 1);
+
+        dest.write_str("shape(")?;
+        if !is_default(&self.fill) {
+            self.fill.to_css(dest)?;
+            dest.write_char(' ')?;
+        }
+        dest.write_str("from ")?;
+        match self.commands[0] {
+            ShapeCommand::Move {
+                by_to: _,
+                ref point,
+            } => point.to_css(dest)?,
+            _ => unreachable!("The first command must be move"),
+        }
+        dest.write_str(", ")?;
+        {
+            let mut writer = SequenceWriter::new(dest, ", ");
+            for command in self.commands.iter().skip(1) {
+                writer.item(command)?;
+            }
+        }
+        dest.write_char(')')
+    }
+}
+
+/// This is a more general shape(path) command type, for both shape() and path().
+///
+/// https://www.w3.org/TR/SVG11/paths.html#PathData
+/// https://drafts.csswg.org/css-shapes-2/#shape-function
+#[derive(
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    Deserialize,
+    MallocSizeOf,
+    PartialEq,
+    Serialize,
+    SpecifiedValueInfo,
+    ToAnimatedValue,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[allow(missing_docs)]
+#[repr(C, u8)]
+pub enum GenericShapeCommand<Angle, LengthPercentage> {
+    /// The move command.
+    Move {
+        by_to: ByTo,
+        point: CoordinatePair<LengthPercentage>,
+    },
+    /// The line command.
+    Line {
+        by_to: ByTo,
+        point: CoordinatePair<LengthPercentage>,
+    },
+    /// The hline command.
+    HLine { by_to: ByTo, x: LengthPercentage },
+    /// The vline command.
+    VLine { by_to: ByTo, y: LengthPercentage },
+    /// The cubic Bézier curve command.
+    CubicCurve {
+        by_to: ByTo,
+        point: CoordinatePair<LengthPercentage>,
+        control1: CoordinatePair<LengthPercentage>,
+        control2: CoordinatePair<LengthPercentage>,
+    },
+    /// The quadratic Bézier curve command.
+    QuadCurve {
+        by_to: ByTo,
+        point: CoordinatePair<LengthPercentage>,
+        control1: CoordinatePair<LengthPercentage>,
+    },
+    /// The smooth command.
+    SmoothCubic {
+        by_to: ByTo,
+        point: CoordinatePair<LengthPercentage>,
+        control2: CoordinatePair<LengthPercentage>,
+    },
+    /// The smooth quadratic Bézier curve command.
+    SmoothQuad {
+        by_to: ByTo,
+        point: CoordinatePair<LengthPercentage>,
+    },
+    /// The arc command.
+    Arc {
+        by_to: ByTo,
+        point: CoordinatePair<LengthPercentage>,
+        radii: CoordinatePair<LengthPercentage>,
+        arc_sweep: ArcSweep,
+        arc_size: ArcSize,
+        rotate: Angle,
+    },
+    /// The closepath command.
+    Close,
+}
+
+pub use self::GenericShapeCommand as ShapeCommand;
+
+impl<Angle, LengthPercentage> ToCss for ShapeCommand<Angle, LengthPercentage>
+where
+    Angle: ToCss + Zero,
+    LengthPercentage: PartialEq + ToCss,
+{
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: fmt::Write,
+    {
+        use self::ShapeCommand::*;
+        match *self {
+            Move { by_to, ref point } => {
+                dest.write_str("move ")?;
+                by_to.to_css(dest)?;
+                dest.write_char(' ')?;
+                point.to_css(dest)
+            },
+            Line { by_to, ref point } => {
+                dest.write_str("line ")?;
+                by_to.to_css(dest)?;
+                dest.write_char(' ')?;
+                point.to_css(dest)
+            },
+            HLine { by_to, ref x } => {
+                dest.write_str("hline ")?;
+                by_to.to_css(dest)?;
+                dest.write_char(' ')?;
+                x.to_css(dest)
+            },
+            VLine { by_to, ref y } => {
+                dest.write_str("vline ")?;
+                by_to.to_css(dest)?;
+                dest.write_char(' ')?;
+                y.to_css(dest)
+            },
+            CubicCurve {
+                by_to,
+                ref point,
+                ref control1,
+                ref control2,
+            } => {
+                dest.write_str("curve ")?;
+                by_to.to_css(dest)?;
+                dest.write_char(' ')?;
+                point.to_css(dest)?;
+                dest.write_str(" via ")?;
+                control1.to_css(dest)?;
+                dest.write_char(' ')?;
+                control2.to_css(dest)
+            },
+            QuadCurve {
+                by_to,
+                ref point,
+                ref control1,
+            } => {
+                dest.write_str("curve ")?;
+                by_to.to_css(dest)?;
+                dest.write_char(' ')?;
+                point.to_css(dest)?;
+                dest.write_str(" via ")?;
+                control1.to_css(dest)
+            },
+            SmoothCubic {
+                by_to,
+                ref point,
+                ref control2,
+            } => {
+                dest.write_str("smooth ")?;
+                by_to.to_css(dest)?;
+                dest.write_char(' ')?;
+                point.to_css(dest)?;
+                dest.write_str(" via ")?;
+                control2.to_css(dest)
+            },
+            SmoothQuad { by_to, ref point } => {
+                dest.write_str("smooth ")?;
+                by_to.to_css(dest)?;
+                dest.write_char(' ')?;
+                point.to_css(dest)
+            },
+            Arc {
+                by_to,
+                ref point,
+                ref radii,
+                arc_sweep,
+                arc_size,
+                ref rotate,
+            } => {
+                dest.write_str("arc ")?;
+                by_to.to_css(dest)?;
+                dest.write_char(' ')?;
+                point.to_css(dest)?;
+                dest.write_str(" of ")?;
+                radii.x.to_css(dest)?;
+                if radii.x != radii.y {
+                    dest.write_char(' ')?;
+                    radii.y.to_css(dest)?;
+                }
+
+                if matches!(arc_sweep, ArcSweep::Cw) {
+                    dest.write_str(" cw")?;
+                }
+
+                if matches!(arc_size, ArcSize::Large) {
+                    dest.write_str(" large")?;
+                }
+
+                if !rotate.is_zero() {
+                    dest.write_str(" rotate ")?;
+                    rotate.to_css(dest)?;
+                }
+                Ok(())
+            },
+            Close => dest.write_str("close"),
+        }
+    }
+}
+
+/// This indicates the command is absolute or relative.
+/// https://drafts.csswg.org/css-shapes-2/#typedef-shape-by-to
+#[derive(
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    Deserialize,
+    MallocSizeOf,
+    Parse,
+    PartialEq,
+    Serialize,
+    SpecifiedValueInfo,
+    ToAnimatedValue,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(u8)]
+pub enum ByTo {
+    /// This indicates that the <coordinate-pair>s are relative to the command’s starting point.
+    By,
+    /// This relative to the top-left corner of the reference box.
+    To,
+}
+
+impl ByTo {
+    /// Return true if it is absolute, i.e. it is To.
+    #[inline]
+    pub fn is_abs(&self) -> bool {
+        matches!(self, ByTo::To)
+    }
+
+    /// Create ByTo based on the flag if it is absolute.
+    #[inline]
+    pub fn new(is_abs: bool) -> Self {
+        if is_abs {
+            Self::To
+        } else {
+            Self::By
+        }
+    }
+}
+
+/// Defines a pair of coordinates, representing a rightward and downward offset, respectively, from
+/// a specified reference point. Percentages are resolved against the width or height,
+/// respectively, of the reference box.
+/// https://drafts.csswg.org/css-shapes-2/#typedef-shape-coordinate-pair
+#[allow(missing_docs)]
+#[derive(
+    AddAssign,
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    Deserialize,
+    MallocSizeOf,
+    PartialEq,
+    Serialize,
+    SpecifiedValueInfo,
+    ToAnimatedValue,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C)]
+pub struct CoordinatePair<LengthPercentage> {
+    pub x: LengthPercentage,
+    pub y: LengthPercentage,
+}
+
+impl<LengthPercentage> CoordinatePair<LengthPercentage> {
+    /// Create a CoordinatePair.
+    #[inline]
+    pub fn new(x: LengthPercentage, y: LengthPercentage) -> Self {
+        Self { x, y }
+    }
+}
+
+/// This indicates that the arc that is traced around the ellipse clockwise or counter-clockwise
+/// from the center.
+/// https://drafts.csswg.org/css-shapes-2/#typedef-shape-arc-sweep
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    Deserialize,
+    FromPrimitive,
+    MallocSizeOf,
+    Parse,
+    PartialEq,
+    Serialize,
+    SpecifiedValueInfo,
+    ToAnimatedValue,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(u8)]
+pub enum ArcSweep {
+    /// Counter-clockwise. The default value. (This also represents 0 in the svg path.)
+    Ccw = 0,
+    /// Clockwise. (This also represents 1 in the svg path.)
+    Cw = 1,
+}
+
+impl Animate for ArcSweep {
+    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
+        use num_traits::FromPrimitive;
+        // If an arc command has different <arc-sweep> between its starting and ending list, then
+        // the interpolated result uses cw for any progress value between 0 and 1.
+        (*self as i32)
+            .animate(&(*other as i32), procedure)
+            .map(|v| ArcSweep::from_u8((v > 0) as u8).unwrap_or(ArcSweep::Ccw))
+    }
+}
+
+impl ComputeSquaredDistance for ArcSweep {
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        (*self as i32).compute_squared_distance(&(*other as i32))
+    }
+}
+
+/// This indicates that the larger or smaller, respectively, of the two possible arcs must be
+/// chosen.
+/// https://drafts.csswg.org/css-shapes-2/#typedef-shape-arc-size
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    Deserialize,
+    FromPrimitive,
+    MallocSizeOf,
+    Parse,
+    PartialEq,
+    Serialize,
+    SpecifiedValueInfo,
+    ToAnimatedValue,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(u8)]
+pub enum ArcSize {
+    /// Choose the small one. The default value. (This also represents 0 in the svg path.)
+    Small = 0,
+    /// Choose the large one. (This also represents 1 in the svg path.)
+    Large = 1,
+}
+
+impl Animate for ArcSize {
+    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
+        use num_traits::FromPrimitive;
+        // If it has different <arc-size> keywords, then the interpolated result uses large for any
+        // progress value between 0 and 1.
+        (*self as i32)
+            .animate(&(*other as i32), procedure)
+            .map(|v| ArcSize::from_u8((v > 0) as u8).unwrap_or(ArcSize::Small))
+    }
+}
+
+impl ComputeSquaredDistance for ArcSize {
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        (*self as i32).compute_squared_distance(&(*other as i32))
+    }
+}
diff --git a/servo/components/style/values/generics/counters.rs b/servo/components/style/values/generics/counters.rs
index 1d4518c57b..3f23c74b33 100644
--- a/servo/components/style/values/generics/counters.rs
+++ b/servo/components/style/values/generics/counters.rs
@@ -4,11 +4,10 @@
 
 //! Generic types for counters-related CSS values.
 
-#[cfg(feature = "servo-layout-2013")]
+#[cfg(feature = "servo")]
 use crate::computed_values::list_style_type::T as ListStyleType;
 #[cfg(feature = "gecko")]
 use crate::values::generics::CounterStyle;
-#[cfg(any(feature = "gecko", feature = "servo-layout-2020"))]
 use crate::values::specified::Attr;
 use crate::values::CustomIdent;
 use std::fmt::{self, Write};
@@ -186,13 +185,13 @@ pub struct GenericCounters<I>(
 );
 pub use self::GenericCounters as Counters;
 
-#[cfg(feature = "servo-layout-2013")]
+#[cfg(feature = "servo")]
 type CounterStyleType = ListStyleType;
 
 #[cfg(feature = "gecko")]
 type CounterStyleType = CounterStyle;
 
-#[cfg(feature = "servo-layout-2013")]
+#[cfg(feature = "servo")]
 #[inline]
 fn is_decimal(counter_type: &CounterStyleType) -> bool {
     *counter_type == ListStyleType::Decimal
@@ -254,11 +253,9 @@ pub enum GenericContentItem<I> {
     /// Literal string content.
     String(crate::OwnedStr),
     /// `counter(name, style)`.
-    #[cfg(any(feature = "gecko", feature = "servo-layout-2013"))]
     #[css(comma, function)]
     Counter(CustomIdent, #[css(skip_if = "is_decimal")] CounterStyleType),
     /// `counters(name, separator, style)`.
-    #[cfg(any(feature = "gecko", feature = "servo-layout-2013"))]
     #[css(comma, function)]
     Counters(
         CustomIdent,
@@ -266,16 +263,12 @@ pub enum GenericContentItem<I> {
         #[css(skip_if = "is_decimal")] CounterStyleType,
     ),
     /// `open-quote`.
-    #[cfg(any(feature = "gecko", feature = "servo-layout-2013"))]
     OpenQuote,
     /// `close-quote`.
-    #[cfg(any(feature = "gecko", feature = "servo-layout-2013"))]
     CloseQuote,
     /// `no-open-quote`.
-    #[cfg(any(feature = "gecko", feature = "servo-layout-2013"))]
     NoOpenQuote,
     /// `no-close-quote`.
-    #[cfg(any(feature = "gecko", feature = "servo-layout-2013"))]
     NoCloseQuote,
     /// `-moz-alt-content`.
     #[cfg(feature = "gecko")]
@@ -286,7 +279,6 @@ pub enum GenericContentItem<I> {
     #[cfg(feature = "gecko")]
     MozLabelContent,
     /// `attr([namespace? `|`]? ident)`
-    #[cfg(any(feature = "gecko", feature = "servo-layout-2020"))]
     Attr(Attr),
     /// image-set(url) | url(url)
     Image(I),
diff --git a/servo/components/style/values/generics/image.rs b/servo/components/style/values/generics/image.rs
index 6fc0870e15..ca1c716052 100644
--- a/servo/components/style/values/generics/image.rs
+++ b/servo/components/style/values/generics/image.rs
@@ -41,7 +41,7 @@ pub enum GenericImage<G, ImageUrl, Color, Percentage, Resolution> {
 
     /// A paint worklet image.
     /// <https://drafts.css-houdini.org/css-paint-api/>
-    #[cfg(feature = "servo-layout-2013")]
+    #[cfg(feature = "servo")]
     PaintWorklet(PaintWorklet),
 
     /// A `<cross-fade()>` image. Storing this directly inside of
@@ -416,7 +416,7 @@ where
             Image::None => dest.write_str("none"),
             Image::Url(ref url) => url.to_css(dest),
             Image::Gradient(ref gradient) => gradient.to_css(dest),
-            #[cfg(feature = "servo-layout-2013")]
+            #[cfg(feature = "servo")]
             Image::PaintWorklet(ref paint_worklet) => paint_worklet.to_css(dest),
             #[cfg(feature = "gecko")]
             Image::Element(ref selector) => {
diff --git a/servo/components/style/values/generics/transform.rs b/servo/components/style/values/generics/transform.rs
index 3a65c460a7..4d70e4465c 100644
--- a/servo/components/style/values/generics/transform.rs
+++ b/servo/components/style/values/generics/transform.rs
@@ -11,7 +11,6 @@ use crate::values::specified::length::Length as SpecifiedLength;
 use crate::values::specified::length::LengthPercentage as SpecifiedLengthPercentage;
 use crate::values::{computed, CSSFloat};
 use crate::{Zero, ZeroNoPercent};
-use euclid;
 use euclid::default::{Rect, Transform3D};
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ToCss};
diff --git a/servo/components/style/values/resolved/mod.rs b/servo/components/style/values/resolved/mod.rs
index 675f3cca68..d830474fe6 100644
--- a/servo/components/style/values/resolved/mod.rs
+++ b/servo/components/style/values/resolved/mod.rs
@@ -95,7 +95,6 @@ trivial_to_resolved_value!(computed::url::ComputedImageUrl);
 trivial_to_resolved_value!(crate::Namespace);
 #[cfg(feature = "servo")]
 trivial_to_resolved_value!(crate::Prefix);
-trivial_to_resolved_value!(computed::LengthPercentage);
 trivial_to_resolved_value!(style_traits::values::specified::AllowedNumericType);
 trivial_to_resolved_value!(computed::TimingFunction);
 
diff --git a/servo/components/style/values/specified/animation.rs b/servo/components/style/values/specified/animation.rs
index 5a1f5003f3..552521711c 100644
--- a/servo/components/style/values/specified/animation.rs
+++ b/servo/components/style/values/specified/animation.rs
@@ -165,6 +165,12 @@ impl AnimationIterationCount {
     pub fn one() -> Self {
         Self::Number(NonNegativeNumber::new(1.0))
     }
+
+    /// Returns true if it's `1.0`.
+    #[inline]
+    pub fn is_one(&self) -> bool {
+        *self == Self::one()
+    }
 }
 
 /// A value for the `animation-name` property.
@@ -230,6 +236,17 @@ pub enum AnimationDirection {
     AlternateReverse,
 }
 
+impl AnimationDirection {
+    /// Returns true if the name matches any animation-direction keyword.
+    #[inline]
+    pub fn match_keywords(name: &AnimationName) -> bool {
+        if let Some(name) = name.as_atom() {
+            return name.with_str(|n| Self::from_ident(n).is_ok());
+        }
+        false
+    }
+}
+
 /// https://drafts.csswg.org/css-animations/#animation-play-state
 #[derive(Copy, Clone, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss, ToResolvedValue, ToShmem)]
 #[repr(u8)]
@@ -239,6 +256,17 @@ pub enum AnimationPlayState {
     Paused,
 }
 
+impl AnimationPlayState {
+    /// Returns true if the name matches any animation-play-state keyword.
+    #[inline]
+    pub fn match_keywords(name: &AnimationName) -> bool {
+        if let Some(name) = name.as_atom() {
+            return name.with_str(|n| Self::from_ident(n).is_ok());
+        }
+        false
+    }
+}
+
 /// https://drafts.csswg.org/css-animations/#propdef-animation-fill-mode
 #[derive(Copy, Clone, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss, ToResolvedValue, ToShmem)]
 #[repr(u8)]
@@ -250,6 +278,18 @@ pub enum AnimationFillMode {
     Both,
 }
 
+impl AnimationFillMode {
+    /// Returns true if the name matches any animation-fill-mode keyword.
+    /// Note: animation-name:none is its initial value, so we don't have to match none here.
+    #[inline]
+    pub fn match_keywords(name: &AnimationName) -> bool {
+        if let Some(atom) = name.as_atom() {
+            return !name.is_none() && atom.with_str(|n| Self::from_ident(n).is_ok());
+        }
+        false
+    }
+}
+
 /// https://drafts.csswg.org/css-animations-2/#animation-composition
 #[derive(Copy, Clone, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss, ToResolvedValue, ToShmem)]
 #[repr(u8)]
diff --git a/servo/components/style/values/specified/basic_shape.rs b/servo/components/style/values/specified/basic_shape.rs
index 526296b735..8ed32c40c5 100644
--- a/servo/components/style/values/specified/basic_shape.rs
+++ b/servo/components/style/values/specified/basic_shape.rs
@@ -14,6 +14,7 @@ use crate::values::generics::basic_shape as generic;
 use crate::values::generics::basic_shape::{Path, PolygonCoord};
 use crate::values::generics::position::{GenericPosition, GenericPositionOrAuto};
 use crate::values::generics::rect::Rect;
+use crate::values::specified::angle::Angle;
 use crate::values::specified::border::BorderRadius;
 use crate::values::specified::image::Image;
 use crate::values::specified::length::LengthPercentageOrAuto;
@@ -40,6 +41,7 @@ pub type ShapePosition = GenericPosition<LengthPercentage, LengthPercentage>;
 
 /// A specified basic shape.
 pub type BasicShape = generic::GenericBasicShape<
+    Angle,
     ShapePosition,
     LengthPercentage,
     NonNegativeLengthPercentage,
@@ -61,6 +63,12 @@ pub type ShapeRadius = generic::ShapeRadius<NonNegativeLengthPercentage>;
 /// The specified value of `Polygon`.
 pub type Polygon = generic::GenericPolygon<LengthPercentage>;
 
+/// The specified value of `PathOrShapeFunction`.
+pub type PathOrShapeFunction = generic::GenericPathOrShapeFunction<Angle, LengthPercentage>;
+
+/// The specified value of `ShapeCommand`.
+pub type ShapeCommand = generic::GenericShapeCommand<Angle, LengthPercentage>;
+
 /// The specified value of `xywh()`.
 /// Defines a rectangle via offsets from the top and left edge of the reference box, and a
 /// specified width and height.
@@ -168,8 +176,8 @@ bitflags! {
         const POLYGON = 1 << 5;
         /// path().
         const PATH = 1 << 6;
-        // TODO: Bug 1823463. Add shape().
-        // const SHAPE = 1 << 7;
+        /// shape().
+        const SHAPE = 1 << 7;
 
         /// All flags.
         const ALL =
@@ -179,7 +187,8 @@ bitflags! {
             Self::CIRCLE.bits() |
             Self::ELLIPSE.bits() |
             Self::POLYGON.bits() |
-            Self::PATH.bits();
+            Self::PATH.bits() |
+            Self::SHAPE.bits();
 
         /// For shape-outside.
         const SHAPE_OUTSIDE =
@@ -329,7 +338,17 @@ impl BasicShape {
                         .map(BasicShape::Polygon)
                 },
                 "path" if flags.contains(AllowedBasicShapes::PATH) => {
-                    Path::parse_function_arguments(i, shape_type).map(BasicShape::Path)
+                    Path::parse_function_arguments(i, shape_type)
+                        .map(PathOrShapeFunction::Path)
+                        .map(BasicShape::PathOrShape)
+                },
+                "shape"
+                    if flags.contains(AllowedBasicShapes::SHAPE)
+                        && static_prefs::pref!("layout.css.basic-shape-shape.enabled") =>
+                {
+                    generic::Shape::parse_function_arguments(context, i, shape_type)
+                        .map(PathOrShapeFunction::Shape)
+                        .map(BasicShape::PathOrShape)
                 },
                 _ => Err(location
                     .new_custom_error(StyleParseErrorKind::UnexpectedFunction(function.clone()))),
@@ -490,7 +509,11 @@ impl Ellipse {
     }
 }
 
-fn parse_fill_rule<'i, 't>(input: &mut Parser<'i, 't>, shape_type: ShapeType) -> FillRule {
+fn parse_fill_rule<'i, 't>(
+    input: &mut Parser<'i, 't>,
+    shape_type: ShapeType,
+    expect_comma: bool,
+) -> FillRule {
     match shape_type {
         // Per [1] and [2], we ignore `<fill-rule>` for outline shapes, so always use a default
         // value.
@@ -508,7 +531,9 @@ fn parse_fill_rule<'i, 't>(input: &mut Parser<'i, 't>, shape_type: ShapeType) ->
         ShapeType::Filled => input
             .try_parse(|i| -> Result<_, ParseError> {
                 let fill = FillRule::parse(i)?;
-                i.expect_comma()?;
+                if expect_comma {
+                    i.expect_comma()?;
+                }
                 Ok(fill)
             })
             .unwrap_or_default(),
@@ -532,7 +557,7 @@ impl Polygon {
         input: &mut Parser<'i, 't>,
         shape_type: ShapeType,
     ) -> Result<Self, ParseError<'i>> {
-        let fill = parse_fill_rule(input, shape_type);
+        let fill = parse_fill_rule(input, shape_type, true /* has comma */);
         let coordinates = input
             .parse_comma_separated(|i| {
                 Ok(PolygonCoord(
@@ -554,7 +579,7 @@ impl Path {
     ) -> Result<Self, ParseError<'i>> {
         use crate::values::specified::svg_path::AllowEmpty;
 
-        let fill = parse_fill_rule(input, shape_type);
+        let fill = parse_fill_rule(input, shape_type, true /* has comma */);
         let path = SVGPathData::parse(input, AllowEmpty::No)?;
         Ok(Path { fill, path })
     }
@@ -717,3 +742,168 @@ impl ToComputedValue for BasicShapeRect {
         Self::Inset(ToComputedValue::from_computed_value(computed))
     }
 }
+
+impl generic::Shape<Angle, LengthPercentage> {
+    /// Parse the inner arguments of a `shape` function.
+    /// shape() = shape(<fill-rule>? from <coordinate-pair>, <shape-command>#)
+    fn parse_function_arguments<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        shape_type: ShapeType,
+    ) -> Result<Self, ParseError<'i>> {
+        let fill = parse_fill_rule(input, shape_type, false /* no following comma */);
+
+        let mut first = true;
+        let commands = input.parse_comma_separated(|i| {
+            if first {
+                first = false;
+
+                // The starting point for the first shape-command. It adds an initial absolute
+                // moveto to the list of path data commands, with the <coordinate-pair> measured
+                // from the top-left corner of the reference
+                i.expect_ident_matching("from")?;
+                Ok(ShapeCommand::Move {
+                    by_to: generic::ByTo::To,
+                    point: generic::CoordinatePair::parse(context, i)?,
+                })
+            } else {
+                // The further path data commands.
+                ShapeCommand::parse(context, i)
+            }
+        })?;
+
+        // We must have one starting point and at least one following <shape-command>.
+        if commands.len() < 2 {
+            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+        }
+
+        Ok(Self {
+            fill,
+            commands: commands.into(),
+        })
+    }
+}
+
+impl Parse for ShapeCommand {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        use crate::values::generics::basic_shape::{ArcSize, ArcSweep, ByTo, CoordinatePair};
+
+        // <shape-command> = <move-command> | <line-command> | <hv-line-command> |
+        //                   <curve-command> | <smooth-command> | <arc-command> | close
+        Ok(try_match_ident_ignore_ascii_case! { input,
+            "close" => Self::Close,
+            "move" => {
+                let by_to = ByTo::parse(input)?;
+                let point = CoordinatePair::parse(context, input)?;
+                Self::Move { by_to, point }
+            },
+            "line" => {
+                let by_to = ByTo::parse(input)?;
+                let point = CoordinatePair::parse(context, input)?;
+                Self::Line { by_to, point }
+            },
+            "hline" => {
+                let by_to = ByTo::parse(input)?;
+                let x = LengthPercentage::parse(context, input)?;
+                Self::HLine { by_to, x }
+            },
+            "vline" => {
+                let by_to = ByTo::parse(input)?;
+                let y = LengthPercentage::parse(context, input)?;
+                Self::VLine { by_to, y }
+            },
+            "curve" => {
+                let by_to = ByTo::parse(input)?;
+                let point = CoordinatePair::parse(context, input)?;
+                input.expect_ident_matching("via")?;
+                let control1 = CoordinatePair::parse(context, input)?;
+                match input.try_parse(|i| CoordinatePair::parse(context, i)) {
+                    Ok(control2) => Self::CubicCurve {
+                        by_to,
+                        point,
+                        control1,
+                        control2,
+                    },
+                    Err(_) => Self::QuadCurve {
+                        by_to,
+                        point,
+                        control1,
+                    },
+                }
+            },
+            "smooth" => {
+                let by_to = ByTo::parse(input)?;
+                let point = CoordinatePair::parse(context, input)?;
+                if input.try_parse(|i| i.expect_ident_matching("via")).is_ok() {
+                    let control2 = CoordinatePair::parse(context, input)?;
+                    Self::SmoothCubic {
+                        by_to,
+                        point,
+                        control2,
+                    }
+                } else {
+                    Self::SmoothQuad { by_to, point }
+                }
+            },
+            "arc" => {
+                let by_to = ByTo::parse(input)?;
+                let point = CoordinatePair::parse(context, input)?;
+                input.expect_ident_matching("of")?;
+                let rx = LengthPercentage::parse(context, input)?;
+                let ry = input
+                    .try_parse(|i| LengthPercentage::parse(context, i))
+                    .unwrap_or(rx.clone());
+                let radii = CoordinatePair::new(rx, ry);
+
+                // [<arc-sweep> || <arc-size> || rotate <angle>]?
+                let mut arc_sweep = None;
+                let mut arc_size = None;
+                let mut rotate = None;
+                loop {
+                    if arc_sweep.is_none() {
+                        arc_sweep = input.try_parse(ArcSweep::parse).ok();
+                    }
+
+                    if arc_size.is_none() {
+                        arc_size = input.try_parse(ArcSize::parse).ok();
+                        if arc_size.is_some() {
+                            continue;
+                        }
+                    }
+
+                    if rotate.is_none()
+                        && input
+                            .try_parse(|i| i.expect_ident_matching("rotate"))
+                            .is_ok()
+                    {
+                        rotate = Some(Angle::parse(context, input)?);
+                        continue;
+                    }
+                    break;
+                }
+                Self::Arc {
+                    by_to,
+                    point,
+                    radii,
+                    arc_sweep: arc_sweep.unwrap_or(ArcSweep::Ccw),
+                    arc_size: arc_size.unwrap_or(ArcSize::Small),
+                    rotate: rotate.unwrap_or(Angle::zero()),
+                }
+            },
+        })
+    }
+}
+
+impl Parse for generic::CoordinatePair<LengthPercentage> {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let x = LengthPercentage::parse(context, input)?;
+        let y = LengthPercentage::parse(context, input)?;
+        Ok(Self::new(x, y))
+    }
+}
diff --git a/servo/components/style/values/specified/box.rs b/servo/components/style/values/specified/box.rs
index 8414591c2b..ee50227504 100644
--- a/servo/components/style/values/specified/box.rs
+++ b/servo/components/style/values/specified/box.rs
@@ -19,12 +19,12 @@ use std::fmt::{self, Write};
 use style_traits::{CssWriter, KeywordsCollectFn, ParseError};
 use style_traits::{SpecifiedValueInfo, StyleParseErrorKind, ToCss};
 
-#[cfg(not(feature = "servo-layout-2020"))]
+#[cfg(not(feature = "servo"))]
 fn flexbox_enabled() -> bool {
     true
 }
 
-#[cfg(feature = "servo-layout-2020")]
+#[cfg(feature = "servo")]
 fn flexbox_enabled() -> bool {
     servo_config::prefs::pref_map()
         .get("layout.flexbox.enabled")
@@ -42,9 +42,7 @@ pub enum DisplayOutside {
     None = 0,
     Inline,
     Block,
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     TableCaption,
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     InternalTable,
     #[cfg(feature = "gecko")]
     InternalRuby,
@@ -55,28 +53,19 @@ pub enum DisplayOutside {
 #[repr(u8)]
 pub enum DisplayInside {
     None = 0,
-    #[cfg(any(feature = "servo-layout-2020", feature = "gecko"))]
     Contents,
     Flow,
     FlowRoot,
     Flex,
     #[cfg(feature = "gecko")]
     Grid,
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     Table,
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     TableRowGroup,
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     TableColumn,
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     TableColumnGroup,
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     TableHeaderGroup,
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     TableFooterGroup,
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     TableRow,
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     TableCell,
     #[cfg(feature = "gecko")]
     Ruby,
@@ -145,7 +134,6 @@ impl Display {
     /// ::new() inlined so cbindgen can use it
     pub const None: Self =
         Self(((DisplayOutside::None as u16) << Self::OUTSIDE_SHIFT) | DisplayInside::None as u16);
-    #[cfg(any(feature = "servo-layout-2020", feature = "gecko"))]
     pub const Contents: Self = Self(
         ((DisplayOutside::None as u16) << Self::OUTSIDE_SHIFT) | DisplayInside::Contents as u16,
     );
@@ -170,14 +158,11 @@ impl Display {
     #[cfg(feature = "gecko")]
     pub const InlineGrid: Self =
         Self(((DisplayOutside::Inline as u16) << Self::OUTSIDE_SHIFT) | DisplayInside::Grid as u16);
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     pub const Table: Self =
         Self(((DisplayOutside::Block as u16) << Self::OUTSIDE_SHIFT) | DisplayInside::Table as u16);
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     pub const InlineTable: Self = Self(
         ((DisplayOutside::Inline as u16) << Self::OUTSIDE_SHIFT) | DisplayInside::Table as u16,
     );
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     pub const TableCaption: Self = Self(
         ((DisplayOutside::TableCaption as u16) << Self::OUTSIDE_SHIFT) | DisplayInside::Flow as u16,
     );
@@ -195,37 +180,30 @@ impl Display {
 
     // Internal table boxes.
 
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     pub const TableRowGroup: Self = Self(
         ((DisplayOutside::InternalTable as u16) << Self::OUTSIDE_SHIFT) |
             DisplayInside::TableRowGroup as u16,
     );
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     pub const TableHeaderGroup: Self = Self(
         ((DisplayOutside::InternalTable as u16) << Self::OUTSIDE_SHIFT) |
             DisplayInside::TableHeaderGroup as u16,
     );
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     pub const TableFooterGroup: Self = Self(
         ((DisplayOutside::InternalTable as u16) << Self::OUTSIDE_SHIFT) |
             DisplayInside::TableFooterGroup as u16,
     );
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     pub const TableColumn: Self = Self(
         ((DisplayOutside::InternalTable as u16) << Self::OUTSIDE_SHIFT) |
             DisplayInside::TableColumn as u16,
     );
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     pub const TableColumnGroup: Self = Self(
         ((DisplayOutside::InternalTable as u16) << Self::OUTSIDE_SHIFT) |
             DisplayInside::TableColumnGroup as u16,
     );
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     pub const TableRow: Self = Self(
         ((DisplayOutside::InternalTable as u16) << Self::OUTSIDE_SHIFT) |
             DisplayInside::TableRow as u16,
     );
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     pub const TableCell: Self = Self(
         ((DisplayOutside::InternalTable as u16) << Self::OUTSIDE_SHIFT) |
             DisplayInside::TableCell as u16,
@@ -336,7 +314,6 @@ impl Display {
     pub fn is_atomic_inline_level(&self) -> bool {
         match *self {
             Display::InlineBlock | Display::InlineFlex => true,
-            #[cfg(any(feature = "servo-layout-2013"))]
             Display::InlineTable => true,
             _ => false,
         }
@@ -373,7 +350,6 @@ impl Display {
     ///
     /// Also used for :root style adjustments.
     pub fn equivalent_block_display(&self, _is_root_element: bool) -> Self {
-        #[cfg(any(feature = "servo-layout-2020", feature = "gecko"))]
         {
             // Special handling for `contents` and `list-item`s on the root element.
             if _is_root_element && (self.is_contents() || self.is_list_item()) {
@@ -392,7 +368,6 @@ impl Display {
                 Display::from3(DisplayOutside::Block, inside, self.is_list_item())
             },
             DisplayOutside::Block | DisplayOutside::None => *self,
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
             _ => Display::Block,
         }
     }
@@ -419,7 +394,6 @@ impl Display {
     #[inline]
     pub fn is_contents(&self) -> bool {
         match *self {
-            #[cfg(any(feature = "servo-layout-2020", feature = "gecko"))]
             Display::Contents => true,
             _ => false,
         }
@@ -444,30 +418,20 @@ impl DisplayKeyword {
         use self::DisplayKeyword::*;
         Ok(try_match_ident_ignore_ascii_case! { input,
             "none" => Full(Display::None),
-            #[cfg(any(feature = "servo-layout-2020", feature = "gecko"))]
             "contents" => Full(Display::Contents),
             "inline-block" => Full(Display::InlineBlock),
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
             "inline-table" => Full(Display::InlineTable),
             "-webkit-flex" if flexbox_enabled() => Full(Display::Flex),
             "inline-flex" | "-webkit-inline-flex" if flexbox_enabled() => Full(Display::InlineFlex),
             #[cfg(feature = "gecko")]
             "inline-grid" => Full(Display::InlineGrid),
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
             "table-caption" => Full(Display::TableCaption),
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
             "table-row-group" => Full(Display::TableRowGroup),
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
             "table-header-group" => Full(Display::TableHeaderGroup),
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
             "table-footer-group" => Full(Display::TableFooterGroup),
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
             "table-column" => Full(Display::TableColumn),
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
             "table-column-group" => Full(Display::TableColumnGroup),
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
             "table-row" => Full(Display::TableRow),
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
             "table-cell" => Full(Display::TableCell),
             #[cfg(feature = "gecko")]
             "ruby-base" => Full(Display::RubyBase),
@@ -493,9 +457,7 @@ impl DisplayKeyword {
             /// https://drafts.csswg.org/css-display/#typedef-display-inside
             "flow" => Inside(DisplayInside::Flow),
             "flex" if flexbox_enabled() => Inside(DisplayInside::Flex),
-            #[cfg(any(feature = "servo-layout-2020", feature = "gecko"))]
             "flow-root" => Inside(DisplayInside::FlowRoot),
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
             "table" => Inside(DisplayInside::Table),
             #[cfg(feature = "gecko")]
             "grid" => Inside(DisplayInside::Grid),
@@ -517,13 +479,11 @@ impl ToCss for Display {
             Display::InlineBlock => dest.write_str("inline-block"),
             #[cfg(feature = "gecko")]
             Display::WebkitInlineBox => dest.write_str("-webkit-inline-box"),
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
             Display::TableCaption => dest.write_str("table-caption"),
             _ => match (outside, inside) {
                 #[cfg(feature = "gecko")]
                 (DisplayOutside::Inline, DisplayInside::Grid) => dest.write_str("inline-grid"),
                 (DisplayOutside::Inline, DisplayInside::Flex) => dest.write_str("inline-flex"),
-                #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
                 (DisplayOutside::Inline, DisplayInside::Table) => dest.write_str("inline-table"),
                 #[cfg(feature = "gecko")]
                 (DisplayOutside::Block, DisplayInside::Ruby) => dest.write_str("block ruby"),
@@ -1607,18 +1567,12 @@ pub enum Appearance {
     TabScrollArrowBack,
     #[parse(condition = "ParserContext::chrome_rules_enabled")]
     TabScrollArrowForward,
-    /// A toolbar in an application window.
-    #[parse(condition = "ParserContext::chrome_rules_enabled")]
-    Toolbar,
     /// A single toolbar button (with no associated dropdown).
     #[parse(condition = "ParserContext::chrome_rules_enabled")]
     Toolbarbutton,
     /// The dropdown portion of a toolbar button
     #[parse(condition = "ParserContext::chrome_rules_enabled")]
     ToolbarbuttonDropdown,
-    /// The toolbox that contains the toolbars.
-    #[parse(condition = "ParserContext::chrome_rules_enabled")]
-    Toolbox,
     /// A tooltip.
     #[parse(condition = "ParserContext::chrome_rules_enabled")]
     Tooltip,
diff --git a/servo/components/style/values/specified/color.rs b/servo/components/style/values/specified/color.rs
index 3694b4e9bc..f823ba7d30 100644
--- a/servo/components/style/values/specified/color.rs
+++ b/servo/components/style/values/specified/color.rs
@@ -7,21 +7,20 @@
 use super::AllowQuirks;
 use crate::color::component::ColorComponent;
 use crate::color::convert::normalize_hue;
-use crate::color::parsing::{self, FromParsedColor, NumberOrAngle, NumberOrPercentage};
+use crate::color::parsing::{
+    self, ColorParser, FromParsedColor, NumberOrAngle, NumberOrPercentage,
+};
 use crate::color::{mix::ColorInterpolationMethod, AbsoluteColor, ColorSpace};
 use crate::media_queries::Device;
 use crate::parser::{Parse, ParserContext};
 use crate::values::computed::{Color as ComputedColor, Context, ToComputedValue};
-use crate::values::generics::calc::CalcUnits;
 use crate::values::generics::color::{
     ColorMixFlags, GenericCaretColor, GenericColorMix, GenericColorOrAuto,
 };
-use crate::values::specified::calc::{CalcNode, Leaf};
 use crate::values::specified::Percentage;
 use crate::values::{normalize, CustomIdent};
 use cssparser::color::OPAQUE;
 use cssparser::{color::PredefinedColorSpace, BasicParseErrorKind, ParseErrorKind, Parser, Token};
-use itoa;
 use std::fmt::{self, Write};
 use std::io::Write as IoWrite;
 use style_traits::{CssType, CssWriter, KeywordsCollectFn, ParseError, StyleParseErrorKind};
@@ -623,156 +622,6 @@ impl FromParsedColor for Color {
     }
 }
 
-struct ColorParser<'a, 'b: 'a>(&'a ParserContext<'b>);
-
-impl<'a, 'b: 'a, 'i: 'a> parsing::ColorParser<'i> for ColorParser<'a, 'b> {
-    type Output = Color;
-
-    fn parse_number_or_angle<'t>(
-        &self,
-        input: &mut Parser<'i, 't>,
-        allow_none: bool,
-    ) -> Result<ColorComponent<NumberOrAngle>, ParseError<'i>> {
-        use crate::values::specified::Angle;
-
-        let location = input.current_source_location();
-        let token = input.next()?.clone();
-        Ok(match token {
-            Token::Ident(ref value) if allow_none && value.eq_ignore_ascii_case("none") => {
-                ColorComponent::None
-            },
-            Token::Dimension {
-                value, ref unit, ..
-            } => {
-                let angle = Angle::parse_dimension(value, unit, /* from_calc = */ false);
-
-                let degrees = match angle {
-                    Ok(angle) => angle.degrees(),
-                    Err(()) => return Err(location.new_unexpected_token_error(token.clone())),
-                };
-
-                ColorComponent::Value(NumberOrAngle::Angle { degrees })
-            },
-            Token::Number { value, .. } => ColorComponent::Value(NumberOrAngle::Number { value }),
-            Token::Function(ref name) => {
-                let function = CalcNode::math_function(self.0, name, location)?;
-                let node = CalcNode::parse(self.0, input, function, CalcUnits::ANGLE)?;
-
-                // If we can resolve the calc node, then use the value.
-                match node.resolve() {
-                    Ok(Leaf::Number(value)) => {
-                        ColorComponent::Value(NumberOrAngle::Number { value })
-                    },
-                    Ok(Leaf::Angle(angle)) => ColorComponent::Value(NumberOrAngle::Angle {
-                        degrees: angle.degrees(),
-                    }),
-                    _ => {
-                        return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError))
-                    },
-                }
-            },
-            t => return Err(location.new_unexpected_token_error(t)),
-        })
-    }
-
-    fn parse_percentage<'t>(
-        &self,
-        input: &mut Parser<'i, 't>,
-        allow_none: bool,
-    ) -> Result<ColorComponent<f32>, ParseError<'i>> {
-        let location = input.current_source_location();
-
-        Ok(match *input.next()? {
-            Token::Ident(ref value) if allow_none && value.eq_ignore_ascii_case("none") => {
-                ColorComponent::None
-            },
-            Token::Percentage { unit_value, .. } => ColorComponent::Value(unit_value),
-            Token::Function(ref name) => {
-                let function = CalcNode::math_function(self.0, name, location)?;
-                let node = CalcNode::parse(self.0, input, function, CalcUnits::PERCENTAGE)?;
-
-                // If we can resolve the calc node, then use the value.
-                let Ok(resolved_leaf) = node.resolve() else {
-                    return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
-                };
-                if let Leaf::Percentage(value) = resolved_leaf {
-                    ColorComponent::Value(value)
-                } else {
-                    return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
-                }
-            },
-            ref t => return Err(location.new_unexpected_token_error(t.clone())),
-        })
-    }
-
-    fn parse_number<'t>(
-        &self,
-        input: &mut Parser<'i, 't>,
-        allow_none: bool,
-    ) -> Result<ColorComponent<f32>, ParseError<'i>> {
-        let location = input.current_source_location();
-
-        Ok(match *input.next()? {
-            Token::Ident(ref value) if allow_none && value.eq_ignore_ascii_case("none") => {
-                ColorComponent::None
-            },
-            Token::Number { value, .. } => ColorComponent::Value(value),
-            Token::Function(ref name) => {
-                let function = CalcNode::math_function(self.0, name, location)?;
-                let node = CalcNode::parse(self.0, input, function, CalcUnits::empty())?;
-
-                // If we can resolve the calc node, then use the value.
-                let Ok(resolved_leaf) = node.resolve() else {
-                    return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
-                };
-                if let Leaf::Number(value) = resolved_leaf {
-                    ColorComponent::Value(value)
-                } else {
-                    return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
-                }
-            },
-            ref t => return Err(location.new_unexpected_token_error(t.clone())),
-        })
-    }
-
-    fn parse_number_or_percentage<'t>(
-        &self,
-        input: &mut Parser<'i, 't>,
-        allow_none: bool,
-    ) -> Result<ColorComponent<NumberOrPercentage>, ParseError<'i>> {
-        let location = input.current_source_location();
-
-        Ok(match *input.next()? {
-            Token::Ident(ref value) if allow_none && value.eq_ignore_ascii_case("none") => {
-                ColorComponent::None
-            },
-            Token::Number { value, .. } => {
-                ColorComponent::Value(NumberOrPercentage::Number { value })
-            },
-            Token::Percentage { unit_value, .. } => {
-                ColorComponent::Value(NumberOrPercentage::Percentage { unit_value })
-            },
-            Token::Function(ref name) => {
-                let function = CalcNode::math_function(self.0, name, location)?;
-                let node = CalcNode::parse(self.0, input, function, CalcUnits::PERCENTAGE)?;
-
-                // If we can resolve the calc node, then use the value.
-                let Ok(resolved_leaf) = node.resolve() else {
-                    return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
-                };
-                if let Leaf::Percentage(unit_value) = resolved_leaf {
-                    ColorComponent::Value(NumberOrPercentage::Percentage { unit_value })
-                } else if let Leaf::Number(value) = resolved_leaf {
-                    ColorComponent::Value(NumberOrPercentage::Number { value })
-                } else {
-                    return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
-                }
-            },
-            ref t => return Err(location.new_unexpected_token_error(t.clone())),
-        })
-    }
-}
-
 /// Whether to preserve authored colors during parsing. That's useful only if we
 /// plan to serialize the color back.
 #[derive(Copy, Clone)]
@@ -809,7 +658,7 @@ impl Color {
             },
         };
 
-        let color_parser = ColorParser(&*context);
+        let color_parser = ColorParser { context: &context };
         match input.try_parse(|i| parsing::parse_color_with(&color_parser, i)) {
             Ok(mut color) => {
                 if let Color::Absolute(ref mut absolute) = color {
diff --git a/servo/components/style/values/specified/counters.rs b/servo/components/style/values/specified/counters.rs
index 9d8261ce6c..7760be91d7 100644
--- a/servo/components/style/values/specified/counters.rs
+++ b/servo/components/style/values/specified/counters.rs
@@ -4,7 +4,7 @@
 
 //! Specified types for counter properties.
 
-#[cfg(feature = "servo-layout-2013")]
+#[cfg(feature = "servo")]
 use crate::computed_values::list_style_type::T as ListStyleType;
 use crate::parser::{Parse, ParserContext};
 use crate::values::generics::counters as generics;
@@ -12,12 +12,10 @@ use crate::values::generics::counters::CounterPair;
 #[cfg(feature = "gecko")]
 use crate::values::generics::CounterStyle;
 use crate::values::specified::image::Image;
-#[cfg(any(feature = "gecko", feature = "servo-layout-2020"))]
 use crate::values::specified::Attr;
 use crate::values::specified::Integer;
 use crate::values::CustomIdent;
 use cssparser::{Parser, Token};
-#[cfg(any(feature = "gecko", feature = "servo-layout-2013"))]
 use selectors::parser::SelectorParseErrorKind;
 use style_traits::{ParseError, StyleParseErrorKind};
 
@@ -151,7 +149,7 @@ pub type Content = generics::GenericContent<Image>;
 pub type ContentItem = generics::GenericContentItem<Image>;
 
 impl Content {
-    #[cfg(feature = "servo-layout-2013")]
+    #[cfg(feature = "servo")]
     fn parse_counter_style(_: &ParserContext, input: &mut Parser) -> ListStyleType {
         input
             .try_parse(|input| {
@@ -197,7 +195,6 @@ impl Parse for Content {
         let mut content = vec![];
         let mut has_alt_content = false;
         loop {
-            #[cfg(any(feature = "gecko", feature = "servo-layout-2020"))]
             {
                 if let Ok(image) = input.try_parse(|i| Image::parse_forbid_none(context, i)) {
                     content.push(generics::ContentItem::Image(image));
@@ -212,13 +209,11 @@ impl Parse for Content {
                 },
                 Ok(&Token::Function(ref name)) => {
                     let result = match_ignore_ascii_case! { &name,
-                        #[cfg(any(feature = "gecko", feature = "servo-layout-2013"))]
                         "counter" => input.parse_nested_block(|input| {
                             let name = CustomIdent::parse(input, &[])?;
                             let style = Content::parse_counter_style(context, input);
                             Ok(generics::ContentItem::Counter(name, style))
                         }),
-                        #[cfg(any(feature = "gecko", feature = "servo-layout-2013"))]
                         "counters" => input.parse_nested_block(|input| {
                             let name = CustomIdent::parse(input, &[])?;
                             input.expect_comma()?;
@@ -226,7 +221,6 @@ impl Parse for Content {
                             let style = Content::parse_counter_style(context, input);
                             Ok(generics::ContentItem::Counters(name, separator, style))
                         }),
-                        #[cfg(any(feature = "gecko", feature = "servo-layout-2020"))]
                         "attr" => input.parse_nested_block(|input| {
                             Ok(generics::ContentItem::Attr(Attr::parse_function(context, input)?))
                         }),
@@ -240,7 +234,6 @@ impl Parse for Content {
                     }?;
                     content.push(result);
                 },
-                #[cfg(any(feature = "gecko", feature = "servo-layout-2013"))]
                 Ok(&Token::Ident(ref ident)) => {
                     content.push(match_ignore_ascii_case! { &ident,
                         "open-quote" => generics::ContentItem::OpenQuote,
diff --git a/servo/components/style/values/specified/easing.rs b/servo/components/style/values/specified/easing.rs
index 5e4d8ae1ea..7697e6a5d7 100644
--- a/servo/components/style/values/specified/easing.rs
+++ b/servo/components/style/values/specified/easing.rs
@@ -9,7 +9,7 @@ use crate::values::computed::easing::TimingFunction as ComputedTimingFunction;
 use crate::values::computed::{Context, ToComputedValue};
 use crate::values::generics::easing::TimingFunction as GenericTimingFunction;
 use crate::values::generics::easing::{StepPosition, TimingKeyword};
-use crate::values::specified::{Integer, Number, Percentage};
+use crate::values::specified::{AnimationName, Integer, Number, Percentage};
 use cssparser::{Delimiter, Parser, Token};
 use selectors::parser::SelectorParseErrorKind;
 use style_traits::{ParseError, StyleParseErrorKind};
@@ -140,6 +140,15 @@ impl TimingFunction {
 
         Ok(GenericTimingFunction::LinearFunction(builder.build()))
     }
+
+    /// Returns true if the name matches any keyword.
+    #[inline]
+    pub fn match_keywords(name: &AnimationName) -> bool {
+        if let Some(name) = name.as_atom() {
+            return name.with_str(|n| TimingKeyword::from_ident(n).is_ok());
+        }
+        false
+    }
 }
 
 // We need this for converting the specified TimingFunction into computed TimingFunction without
diff --git a/servo/components/style/values/specified/effects.rs b/servo/components/style/values/specified/effects.rs
index 0453582768..a32390e148 100644
--- a/servo/components/style/values/specified/effects.rs
+++ b/servo/components/style/values/specified/effects.rs
@@ -28,7 +28,7 @@ use crate::values::specified::{Angle, Number, NumberOrPercentage};
 #[cfg(feature = "servo")]
 use crate::values::Impossible;
 use crate::Zero;
-use cssparser::{self, BasicParseErrorKind, Parser, Token};
+use cssparser::{BasicParseErrorKind, Parser, Token};
 use style_traits::{ParseError, StyleParseErrorKind, ValueParseErrorKind};
 
 /// A specified value for a single shadow of the `box-shadow` property.
diff --git a/servo/components/style/values/specified/image.rs b/servo/components/style/values/specified/image.rs
index 76bbbf85df..bedced1a27 100644
--- a/servo/components/style/values/specified/image.rs
+++ b/servo/components/style/values/specified/image.rs
@@ -241,7 +241,7 @@ impl Image {
         let function = input.expect_function()?.clone();
         input.parse_nested_block(|input| {
             Ok(match_ignore_ascii_case! { &function,
-                #[cfg(feature = "servo-layout-2013")]
+                #[cfg(feature = "servo")]
                 "paint" => Self::PaintWorklet(PaintWorklet::parse_args(context, input)?),
                 "cross-fade" if cross_fade_enabled() => Self::CrossFade(Box::new(CrossFade::parse_args(context, input, cors_mode, flags)?)),
                 #[cfg(feature = "gecko")]
diff --git a/servo/components/style/values/specified/length.rs b/servo/components/style/values/specified/length.rs
index d2e1d7d346..17ff43cd6f 100644
--- a/servo/components/style/values/specified/length.rs
+++ b/servo/components/style/values/specified/length.rs
@@ -97,9 +97,15 @@ pub enum LineHeightBase {
 impl FontBaseSize {
     /// Calculate the actual size for a given context
     pub fn resolve(&self, context: &Context) -> computed::FontSize {
+        let style = context.style();
         match *self {
-            Self::CurrentStyle => context.style().get_font().clone_font_size(),
-            Self::InheritedStyle => context.style().get_parent_font().clone_font_size(),
+            Self::CurrentStyle => style.get_font().clone_font_size(),
+            Self::InheritedStyle => {
+                // If we're using the size from our inherited style, we still need to apply our
+                // own zoom.
+                let zoom = style.get_box().clone_zoom();
+                style.get_parent_font().clone_font_size().zoom(zoom)
+            },
         }
     }
 }
@@ -351,7 +357,7 @@ impl FontRelativeLength {
                 let reference_size = if context.builder.is_root_element || context.in_media_query {
                     reference_font_size.computed_size()
                 } else {
-                    context.device().root_font_size()
+                    context.device().root_font_size().zoom(context.builder.effective_zoom)
                 };
                 (reference_size, length)
             },
@@ -394,19 +400,19 @@ impl FontRelativeLength {
                 //     When specified on the root element, the rlh units refer
                 //     to the initial values of font and line-height properties.
                 //
-                let reference_size: CSSPixelLength =
-                    if context.builder.is_root_element || context.in_media_query {
-                        context
-                            .device()
-                            .calc_line_height(
-                                &context.default_style().get_font(),
-                                context.style().writing_mode,
-                                None,
-                            )
-                            .0
-                    } else {
-                        context.device().root_line_height()
-                    };
+                let reference_size = if context.builder.is_root_element || context.in_media_query {
+                    context
+                        .device()
+                        .calc_line_height(
+                            &context.default_style().get_font(),
+                            context.style().writing_mode,
+                            None,
+                        )
+                        .0
+                } else {
+                    context.device().root_line_height()
+                };
+                let reference_size = reference_size.zoom(context.builder.effective_zoom);
                 (reference_size, length)
             },
         }
@@ -668,7 +674,7 @@ impl ViewportPercentageLength {
     pub fn to_computed_value(&self, context: &Context) -> CSSPixelLength {
         let (variant, unit, factor) = self.unpack();
         let size = context.viewport_size_for_viewport_unit_resolution(variant);
-        let length = match unit {
+        let length: app_units::Au = match unit {
             ViewportUnit::Vw => size.width,
             ViewportUnit::Vh => size.height,
             ViewportUnit::Vmin => cmp::min(size.width, size.height),
@@ -686,13 +692,15 @@ impl ViewportPercentageLength {
             },
         };
 
+        // NOTE: This is in app units!
+        let length = context.builder.effective_zoom.zoom(length.0 as f32);
+
         // FIXME: Bug 1396535, we need to fix the extremely small viewport length for transform.
-        // See bug 989802. We truncate so that adding multiple viewport units
-        // that add up to 100 does not overflow due to rounding differences.
-        // We convert appUnits to CSS px manually here to avoid premature clamping by
-        // going through the Au type.
+        // See bug 989802. We truncate so that adding multiple viewport units that add up to 100
+        // does not overflow due to rounding differences. We convert appUnits to CSS px manually
+        // here to avoid premature clamping by going through the Au type.
         let trunc_scaled =
-            ((length.0 as f64 * factor as f64 / 100.).trunc() / AU_PER_PX as f64) as f32;
+            ((length as f64 * factor as f64 / 100.).trunc() / AU_PER_PX as f64) as f32;
         CSSPixelLength::new(crate::values::normalize(trunc_scaled))
     }
 }
@@ -797,7 +805,7 @@ impl ToComputedValue for AbsoluteLength {
     type ComputedValue = CSSPixelLength;
 
     fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
-        CSSPixelLength::new(context.builder.effective_zoom().zoom(self.to_px())).finite()
+        CSSPixelLength::new(self.to_px()).zoom(context.builder.effective_zoom).finite()
     }
 
     fn from_computed_value(computed: &Self::ComputedValue) -> Self {
@@ -910,6 +918,9 @@ impl ContainerRelativeLength {
             .builder
             .add_flags(ComputedValueFlags::USES_CONTAINER_UNITS);
 
+        // TODO(emilio, bug 1894104): Need to handle zoom here, probably something like
+        // container_zoom - effective_zoom or so. See
+        // https://github.com/w3c/csswg-drafts/issues/10268
         let size = context.get_container_size_query();
         let (factor, container_length) = match *self {
             Self::Cqw(v) => (v, size.get_container_width(context)),
diff --git a/servo/components/style/values/specified/motion.rs b/servo/components/style/values/specified/motion.rs
index 98858c712c..15c76bc640 100644
--- a/servo/components/style/values/specified/motion.rs
+++ b/servo/components/style/values/specified/motion.rs
@@ -76,10 +76,6 @@ impl Parse for RayFunction {
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Self, ParseError<'i>> {
-        if !static_prefs::pref!("layout.css.motion-path-ray.enabled") {
-            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
-        }
-
         input.expect_function_matching("ray")?;
         input.parse_nested_block(|i| Self::parse_function_arguments(context, i))
     }
@@ -154,11 +150,8 @@ impl Parse for OffsetPathFunction {
 
         // <offset-path> = <ray()> | <url> | <basic-shape>
         // https://drafts.fxtf.org/motion-1/#typedef-offset-path
-
-        if static_prefs::pref!("layout.css.motion-path-ray.enabled") {
-            if let Ok(ray) = input.try_parse(|i| RayFunction::parse(context, i)) {
-                return Ok(OffsetPathFunction::Ray(ray));
-            }
+        if let Ok(ray) = input.try_parse(|i| RayFunction::parse(context, i)) {
+            return Ok(OffsetPathFunction::Ray(ray));
         }
 
         if static_prefs::pref!("layout.css.motion-path-url.enabled") {
@@ -167,13 +160,7 @@ impl Parse for OffsetPathFunction {
             }
         }
 
-        let allowed_shapes = if static_prefs::pref!("layout.css.motion-path-basic-shapes.enabled") {
-            AllowedBasicShapes::ALL
-        } else {
-            AllowedBasicShapes::PATH
-        };
-
-        BasicShape::parse(context, input, allowed_shapes, ShapeType::Outline)
+        BasicShape::parse(context, input, AllowedBasicShapes::ALL, ShapeType::Outline)
             .map(OffsetPathFunction::Shape)
     }
 }
@@ -197,9 +184,7 @@ impl Parse for OffsetPath {
                     .ok();
             }
 
-            if static_prefs::pref!("layout.css.motion-path-coord-box.enabled") &&
-                coord_box.is_none()
-            {
+            if coord_box.is_none() {
                 coord_box = input.try_parse(CoordBox::parse).ok();
                 if coord_box.is_some() {
                     continue;
diff --git a/servo/components/style/values/specified/svg_path.rs b/servo/components/style/values/specified/svg_path.rs
index 1eb9866dd1..56342b48bb 100644
--- a/servo/components/style/values/specified/svg_path.rs
+++ b/servo/components/style/values/specified/svg_path.rs
@@ -5,10 +5,13 @@
 //! Specified types for SVG Path.
 
 use crate::parser::{Parse, ParserContext};
-use crate::values::animated::{lists, Animate, Procedure, ToAnimatedZero};
+use crate::values::animated::{lists, Animate, Procedure};
 use crate::values::distance::{ComputeSquaredDistance, SquaredDistance};
+use crate::values::generics::basic_shape::GenericShapeCommand;
+use crate::values::generics::basic_shape::{ArcSize, ArcSweep, ByTo, CoordinatePair};
 use crate::values::CSSFloat;
 use cssparser::Parser;
+use num_traits::FromPrimitive;
 use std::fmt::{self, Write};
 use std::iter::{Cloned, Peekable};
 use std::slice;
@@ -70,6 +73,7 @@ impl SVGPathData {
     #[cfg(feature = "gecko")]
     pub fn decode_from_f32_array(path: &[f32]) -> Result<Self, ()> {
         use crate::gecko_bindings::structs::dom::SVGPathSeg_Binding::*;
+        use crate::values::generics::basic_shape::GenericShapeCommand::*;
 
         let mut result: Vec<PathCommand> = Vec::new();
         let mut i: usize = 0;
@@ -80,85 +84,84 @@ impl SVGPathData {
             let seg_type = path[i].to_bits() as u16;
             i = i + 1;
             match seg_type {
-                PATHSEG_CLOSEPATH => result.push(PathCommand::ClosePath),
+                PATHSEG_CLOSEPATH => result.push(Close),
                 PATHSEG_MOVETO_ABS | PATHSEG_MOVETO_REL => {
                     debug_assert!(i + 1 < path.len());
-                    result.push(PathCommand::MoveTo {
+                    result.push(Move {
                         point: CoordPair::new(path[i], path[i + 1]),
-                        absolute: IsAbsolute::new(seg_type == PATHSEG_MOVETO_ABS),
+                        by_to: ByTo::new(seg_type == PATHSEG_MOVETO_ABS),
                     });
                     i = i + 2;
                 },
                 PATHSEG_LINETO_ABS | PATHSEG_LINETO_REL => {
                     debug_assert!(i + 1 < path.len());
-                    result.push(PathCommand::LineTo {
+                    result.push(Line {
                         point: CoordPair::new(path[i], path[i + 1]),
-                        absolute: IsAbsolute::new(seg_type == PATHSEG_LINETO_ABS),
+                        by_to: ByTo::new(seg_type == PATHSEG_LINETO_ABS),
                     });
                     i = i + 2;
                 },
                 PATHSEG_CURVETO_CUBIC_ABS | PATHSEG_CURVETO_CUBIC_REL => {
                     debug_assert!(i + 5 < path.len());
-                    result.push(PathCommand::CurveTo {
+                    result.push(CubicCurve {
                         control1: CoordPair::new(path[i], path[i + 1]),
                         control2: CoordPair::new(path[i + 2], path[i + 3]),
                         point: CoordPair::new(path[i + 4], path[i + 5]),
-                        absolute: IsAbsolute::new(seg_type == PATHSEG_CURVETO_CUBIC_ABS),
+                        by_to: ByTo::new(seg_type == PATHSEG_CURVETO_CUBIC_ABS),
                     });
                     i = i + 6;
                 },
                 PATHSEG_CURVETO_QUADRATIC_ABS | PATHSEG_CURVETO_QUADRATIC_REL => {
                     debug_assert!(i + 3 < path.len());
-                    result.push(PathCommand::QuadBezierCurveTo {
+                    result.push(QuadCurve {
                         control1: CoordPair::new(path[i], path[i + 1]),
                         point: CoordPair::new(path[i + 2], path[i + 3]),
-                        absolute: IsAbsolute::new(seg_type == PATHSEG_CURVETO_QUADRATIC_ABS),
+                        by_to: ByTo::new(seg_type == PATHSEG_CURVETO_QUADRATIC_ABS),
                     });
                     i = i + 4;
                 },
                 PATHSEG_ARC_ABS | PATHSEG_ARC_REL => {
                     debug_assert!(i + 6 < path.len());
-                    result.push(PathCommand::EllipticalArc {
-                        rx: path[i],
-                        ry: path[i + 1],
-                        angle: path[i + 2],
-                        large_arc_flag: ArcFlag(path[i + 3] != 0.0f32),
-                        sweep_flag: ArcFlag(path[i + 4] != 0.0f32),
+                    result.push(Arc {
+                        radii: CoordPair::new(path[i], path[i + 1]),
+                        rotate: path[i + 2],
+                        arc_size: ArcSize::from_u8((path[i + 3] != 0.0f32) as u8).unwrap(),
+                        arc_sweep: ArcSweep::from_u8((path[i + 4] != 0.0f32) as u8).unwrap(),
                         point: CoordPair::new(path[i + 5], path[i + 6]),
-                        absolute: IsAbsolute::new(seg_type == PATHSEG_ARC_ABS),
+                        by_to: ByTo::new(seg_type == PATHSEG_ARC_ABS),
                     });
                     i = i + 7;
                 },
                 PATHSEG_LINETO_HORIZONTAL_ABS | PATHSEG_LINETO_HORIZONTAL_REL => {
                     debug_assert!(i < path.len());
-                    result.push(PathCommand::HorizontalLineTo {
+                    result.push(HLine {
                         x: path[i],
-                        absolute: IsAbsolute::new(seg_type == PATHSEG_LINETO_HORIZONTAL_ABS),
+                        by_to: ByTo::new(seg_type == PATHSEG_LINETO_HORIZONTAL_ABS),
                     });
                     i = i + 1;
                 },
                 PATHSEG_LINETO_VERTICAL_ABS | PATHSEG_LINETO_VERTICAL_REL => {
                     debug_assert!(i < path.len());
-                    result.push(PathCommand::VerticalLineTo {
+                    result.push(VLine {
                         y: path[i],
-                        absolute: IsAbsolute::new(seg_type == PATHSEG_LINETO_VERTICAL_ABS),
+                        by_to: ByTo::new(seg_type == PATHSEG_LINETO_VERTICAL_ABS),
                     });
                     i = i + 1;
                 },
                 PATHSEG_CURVETO_CUBIC_SMOOTH_ABS | PATHSEG_CURVETO_CUBIC_SMOOTH_REL => {
                     debug_assert!(i + 3 < path.len());
-                    result.push(PathCommand::SmoothCurveTo {
+                    result.push(SmoothCubic {
                         control2: CoordPair::new(path[i], path[i + 1]),
                         point: CoordPair::new(path[i + 2], path[i + 3]),
-                        absolute: IsAbsolute::new(seg_type == PATHSEG_CURVETO_CUBIC_SMOOTH_ABS),
+                        by_to: ByTo::new(seg_type == PATHSEG_CURVETO_CUBIC_SMOOTH_ABS),
                     });
                     i = i + 4;
                 },
                 PATHSEG_CURVETO_QUADRATIC_SMOOTH_ABS | PATHSEG_CURVETO_QUADRATIC_SMOOTH_REL => {
                     debug_assert!(i + 1 < path.len());
-                    result.push(PathCommand::SmoothQuadBezierCurveTo {
+                    result.push(SmoothQuad {
                         point: CoordPair::new(path[i], path[i + 1]),
-                        absolute: IsAbsolute::new(seg_type == PATHSEG_CURVETO_QUADRATIC_SMOOTH_ABS),
+                        by_to: ByTo::new(seg_type == PATHSEG_CURVETO_QUADRATIC_SMOOTH_ABS),
                     });
                     i = i + 2;
                 },
@@ -215,7 +218,7 @@ impl ToCss for SVGPathData {
         {
             let mut writer = SequenceWriter::new(dest, " ");
             for command in self.commands() {
-                writer.item(command)?;
+                writer.write_item(|inner| command.to_css_for_svg(inner))?;
             }
         }
         dest.write_char('"')
@@ -268,79 +271,7 @@ impl ComputeSquaredDistance for SVGPathData {
 /// points of the Bézier curve in the spec.
 ///
 /// https://www.w3.org/TR/SVG11/paths.html#PathData
-#[derive(
-    Animate,
-    Clone,
-    ComputeSquaredDistance,
-    Copy,
-    Debug,
-    Deserialize,
-    MallocSizeOf,
-    PartialEq,
-    Serialize,
-    SpecifiedValueInfo,
-    ToAnimatedZero,
-    ToComputedValue,
-    ToResolvedValue,
-    ToShmem,
-)]
-#[allow(missing_docs)]
-#[repr(C, u8)]
-pub enum PathCommand {
-    /// The unknown type.
-    /// https://www.w3.org/TR/SVG/paths.html#__svg__SVGPathSeg__PATHSEG_UNKNOWN
-    Unknown,
-    /// The "moveto" command.
-    MoveTo {
-        point: CoordPair,
-        absolute: IsAbsolute,
-    },
-    /// The "lineto" command.
-    LineTo {
-        point: CoordPair,
-        absolute: IsAbsolute,
-    },
-    /// The horizontal "lineto" command.
-    HorizontalLineTo { x: CSSFloat, absolute: IsAbsolute },
-    /// The vertical "lineto" command.
-    VerticalLineTo { y: CSSFloat, absolute: IsAbsolute },
-    /// The cubic Bézier curve command.
-    CurveTo {
-        control1: CoordPair,
-        control2: CoordPair,
-        point: CoordPair,
-        absolute: IsAbsolute,
-    },
-    /// The smooth curve command.
-    SmoothCurveTo {
-        control2: CoordPair,
-        point: CoordPair,
-        absolute: IsAbsolute,
-    },
-    /// The quadratic Bézier curve command.
-    QuadBezierCurveTo {
-        control1: CoordPair,
-        point: CoordPair,
-        absolute: IsAbsolute,
-    },
-    /// The smooth quadratic Bézier curve command.
-    SmoothQuadBezierCurveTo {
-        point: CoordPair,
-        absolute: IsAbsolute,
-    },
-    /// The elliptical arc curve command.
-    EllipticalArc {
-        rx: CSSFloat,
-        ry: CSSFloat,
-        angle: CSSFloat,
-        large_arc_flag: ArcFlag,
-        sweep_flag: ArcFlag,
-        point: CoordPair,
-        absolute: IsAbsolute,
-    },
-    /// The "closepath" command.
-    ClosePath,
-}
+pub type PathCommand = GenericShapeCommand<CSSFloat, CSSFloat>;
 
 /// For internal SVGPath normalization.
 #[allow(missing_docs)]
@@ -355,177 +286,157 @@ impl PathCommand {
     ///
     /// See discussion: https://github.com/w3c/svgwg/issues/321
     fn normalize(&self, state: &mut PathTraversalState) -> Self {
-        use self::PathCommand::*;
+        use crate::values::generics::basic_shape::GenericShapeCommand::*;
         match *self {
-            Unknown => Unknown,
-            ClosePath => {
+            Close => {
                 state.pos = state.subpath_start;
-                ClosePath
+                Close
             },
-            MoveTo {
-                mut point,
-                absolute,
-            } => {
-                if !absolute.is_yes() {
+            Move { by_to, mut point } => {
+                if !by_to.is_abs() {
                     point += state.pos;
                 }
                 state.pos = point;
                 state.subpath_start = point;
-                MoveTo {
+                Move {
+                    by_to: ByTo::To,
                     point,
-                    absolute: IsAbsolute::Yes,
                 }
             },
-            LineTo {
-                mut point,
-                absolute,
-            } => {
-                if !absolute.is_yes() {
+            Line { by_to, mut point } => {
+                if !by_to.is_abs() {
                     point += state.pos;
                 }
                 state.pos = point;
-                LineTo {
+                Line {
+                    by_to: ByTo::To,
                     point,
-                    absolute: IsAbsolute::Yes,
                 }
             },
-            HorizontalLineTo { mut x, absolute } => {
-                if !absolute.is_yes() {
+            HLine { by_to, mut x } => {
+                if !by_to.is_abs() {
                     x += state.pos.x;
                 }
                 state.pos.x = x;
-                HorizontalLineTo {
-                    x,
-                    absolute: IsAbsolute::Yes,
-                }
+                HLine { by_to: ByTo::To, x }
             },
-            VerticalLineTo { mut y, absolute } => {
-                if !absolute.is_yes() {
+            VLine { by_to, mut y } => {
+                if !by_to.is_abs() {
                     y += state.pos.y;
                 }
                 state.pos.y = y;
-                VerticalLineTo {
-                    y,
-                    absolute: IsAbsolute::Yes,
-                }
+                VLine { by_to: ByTo::To, y }
             },
-            CurveTo {
+            CubicCurve {
+                by_to,
+                mut point,
                 mut control1,
                 mut control2,
-                mut point,
-                absolute,
             } => {
-                if !absolute.is_yes() {
+                if !by_to.is_abs() {
+                    point += state.pos;
                     control1 += state.pos;
                     control2 += state.pos;
-                    point += state.pos;
                 }
                 state.pos = point;
-                CurveTo {
+                CubicCurve {
+                    by_to: ByTo::To,
+                    point,
                     control1,
                     control2,
-                    point,
-                    absolute: IsAbsolute::Yes,
                 }
             },
-            SmoothCurveTo {
-                mut control2,
+            QuadCurve {
+                by_to,
                 mut point,
-                absolute,
+                mut control1,
             } => {
-                if !absolute.is_yes() {
-                    control2 += state.pos;
+                if !by_to.is_abs() {
                     point += state.pos;
+                    control1 += state.pos;
                 }
                 state.pos = point;
-                SmoothCurveTo {
-                    control2,
+                QuadCurve {
+                    by_to: ByTo::To,
                     point,
-                    absolute: IsAbsolute::Yes,
+                    control1,
                 }
             },
-            QuadBezierCurveTo {
-                mut control1,
+            SmoothCubic {
+                by_to,
                 mut point,
-                absolute,
+                mut control2,
             } => {
-                if !absolute.is_yes() {
-                    control1 += state.pos;
+                if !by_to.is_abs() {
                     point += state.pos;
+                    control2 += state.pos;
                 }
                 state.pos = point;
-                QuadBezierCurveTo {
-                    control1,
+                SmoothCubic {
+                    by_to: ByTo::To,
                     point,
-                    absolute: IsAbsolute::Yes,
+                    control2,
                 }
             },
-            SmoothQuadBezierCurveTo {
-                mut point,
-                absolute,
-            } => {
-                if !absolute.is_yes() {
+            SmoothQuad { by_to, mut point } => {
+                if !by_to.is_abs() {
                     point += state.pos;
                 }
                 state.pos = point;
-                SmoothQuadBezierCurveTo {
+                SmoothQuad {
+                    by_to: ByTo::To,
                     point,
-                    absolute: IsAbsolute::Yes,
                 }
             },
-            EllipticalArc {
-                rx,
-                ry,
-                angle,
-                large_arc_flag,
-                sweep_flag,
+            Arc {
+                by_to,
                 mut point,
-                absolute,
+                radii,
+                arc_sweep,
+                arc_size,
+                rotate,
             } => {
-                if !absolute.is_yes() {
+                if !by_to.is_abs() {
                     point += state.pos;
                 }
                 state.pos = point;
-                EllipticalArc {
-                    rx,
-                    ry,
-                    angle,
-                    large_arc_flag,
-                    sweep_flag,
+                Arc {
+                    by_to: ByTo::To,
                     point,
-                    absolute: IsAbsolute::Yes,
+                    radii,
+                    arc_sweep,
+                    arc_size,
+                    rotate,
                 }
             },
         }
     }
-}
 
-impl ToCss for PathCommand {
-    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    /// The serialization of the svg path.
+    fn to_css_for_svg<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
     where
         W: fmt::Write,
     {
-        use self::PathCommand::*;
+        use crate::values::generics::basic_shape::GenericShapeCommand::*;
         match *self {
-            Unknown => dest.write_char('X'),
-            ClosePath => dest.write_char('Z'),
-            MoveTo { point, absolute } => {
-                dest.write_char(if absolute.is_yes() { 'M' } else { 'm' })?;
+            Close => dest.write_char('Z'),
+            Move { by_to, point } => {
+                dest.write_char(if by_to.is_abs() { 'M' } else { 'm' })?;
                 dest.write_char(' ')?;
                 point.to_css(dest)
             },
-            LineTo { point, absolute } => {
-                dest.write_char(if absolute.is_yes() { 'L' } else { 'l' })?;
+            Line { by_to, point } => {
+                dest.write_char(if by_to.is_abs() { 'L' } else { 'l' })?;
                 dest.write_char(' ')?;
                 point.to_css(dest)
             },
-            CurveTo {
+            CubicCurve {
+                by_to,
+                point,
                 control1,
                 control2,
-                point,
-                absolute,
             } => {
-                dest.write_char(if absolute.is_yes() { 'C' } else { 'c' })?;
+                dest.write_char(if by_to.is_abs() { 'C' } else { 'c' })?;
                 dest.write_char(' ')?;
                 control1.to_css(dest)?;
                 dest.write_char(' ')?;
@@ -533,63 +444,60 @@ impl ToCss for PathCommand {
                 dest.write_char(' ')?;
                 point.to_css(dest)
             },
-            QuadBezierCurveTo {
-                control1,
+            QuadCurve {
+                by_to,
                 point,
-                absolute,
+                control1,
             } => {
-                dest.write_char(if absolute.is_yes() { 'Q' } else { 'q' })?;
+                dest.write_char(if by_to.is_abs() { 'Q' } else { 'q' })?;
                 dest.write_char(' ')?;
                 control1.to_css(dest)?;
                 dest.write_char(' ')?;
                 point.to_css(dest)
             },
-            EllipticalArc {
-                rx,
-                ry,
-                angle,
-                large_arc_flag,
-                sweep_flag,
+            Arc {
+                by_to,
                 point,
-                absolute,
+                radii,
+                arc_sweep,
+                arc_size,
+                rotate,
             } => {
-                dest.write_char(if absolute.is_yes() { 'A' } else { 'a' })?;
-                dest.write_char(' ')?;
-                rx.to_css(dest)?;
+                dest.write_char(if by_to.is_abs() { 'A' } else { 'a' })?;
                 dest.write_char(' ')?;
-                ry.to_css(dest)?;
+                radii.to_css(dest)?;
                 dest.write_char(' ')?;
-                angle.to_css(dest)?;
+                rotate.to_css(dest)?;
                 dest.write_char(' ')?;
-                large_arc_flag.to_css(dest)?;
+                (arc_size as i32).to_css(dest)?;
                 dest.write_char(' ')?;
-                sweep_flag.to_css(dest)?;
+                (arc_sweep as i32).to_css(dest)?;
                 dest.write_char(' ')?;
                 point.to_css(dest)
             },
-            HorizontalLineTo { x, absolute } => {
-                dest.write_char(if absolute.is_yes() { 'H' } else { 'h' })?;
+            HLine { by_to, x } => {
+                dest.write_char(if by_to.is_abs() { 'H' } else { 'h' })?;
                 dest.write_char(' ')?;
                 x.to_css(dest)
             },
-            VerticalLineTo { y, absolute } => {
-                dest.write_char(if absolute.is_yes() { 'V' } else { 'v' })?;
+            VLine { by_to, y } => {
+                dest.write_char(if by_to.is_abs() { 'V' } else { 'v' })?;
                 dest.write_char(' ')?;
                 y.to_css(dest)
             },
-            SmoothCurveTo {
-                control2,
+            SmoothCubic {
+                by_to,
                 point,
-                absolute,
+                control2,
             } => {
-                dest.write_char(if absolute.is_yes() { 'S' } else { 's' })?;
+                dest.write_char(if by_to.is_abs() { 'S' } else { 's' })?;
                 dest.write_char(' ')?;
                 control2.to_css(dest)?;
                 dest.write_char(' ')?;
                 point.to_css(dest)
             },
-            SmoothQuadBezierCurveTo { point, absolute } => {
-                dest.write_char(if absolute.is_yes() { 'T' } else { 't' })?;
+            SmoothQuad { by_to, point } => {
+                dest.write_char(if by_to.is_abs() { 'T' } else { 't' })?;
                 dest.write_char(' ')?;
                 point.to_css(dest)
             },
@@ -597,135 +505,8 @@ impl ToCss for PathCommand {
     }
 }
 
-/// The path command absolute type.
-#[allow(missing_docs)]
-#[derive(
-    Animate,
-    Clone,
-    ComputeSquaredDistance,
-    Copy,
-    Debug,
-    Deserialize,
-    MallocSizeOf,
-    PartialEq,
-    Serialize,
-    SpecifiedValueInfo,
-    ToAnimatedZero,
-    ToComputedValue,
-    ToResolvedValue,
-    ToShmem,
-)]
-#[repr(u8)]
-pub enum IsAbsolute {
-    Yes,
-    No,
-}
-
-impl IsAbsolute {
-    /// Return true if this is IsAbsolute::Yes.
-    #[inline]
-    pub fn is_yes(&self) -> bool {
-        *self == IsAbsolute::Yes
-    }
-
-    /// Return Yes if value is true. Otherwise, return No.
-    #[inline]
-    fn new(value: bool) -> Self {
-        if value {
-            IsAbsolute::Yes
-        } else {
-            IsAbsolute::No
-        }
-    }
-}
-
 /// The path coord type.
-#[allow(missing_docs)]
-#[derive(
-    AddAssign,
-    Animate,
-    Clone,
-    ComputeSquaredDistance,
-    Copy,
-    Debug,
-    Deserialize,
-    MallocSizeOf,
-    PartialEq,
-    Serialize,
-    SpecifiedValueInfo,
-    ToAnimatedZero,
-    ToComputedValue,
-    ToCss,
-    ToResolvedValue,
-    ToShmem,
-)]
-#[repr(C)]
-pub struct CoordPair {
-    x: CSSFloat,
-    y: CSSFloat,
-}
-
-impl CoordPair {
-    /// Create a CoordPair.
-    #[inline]
-    pub fn new(x: CSSFloat, y: CSSFloat) -> Self {
-        CoordPair { x, y }
-    }
-}
-
-/// The EllipticalArc flag type.
-#[derive(
-    Clone,
-    Copy,
-    Debug,
-    Deserialize,
-    MallocSizeOf,
-    PartialEq,
-    Serialize,
-    SpecifiedValueInfo,
-    ToComputedValue,
-    ToResolvedValue,
-    ToShmem,
-)]
-#[repr(C)]
-pub struct ArcFlag(bool);
-
-impl ToCss for ArcFlag {
-    #[inline]
-    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
-    where
-        W: fmt::Write,
-    {
-        (self.0 as i32).to_css(dest)
-    }
-}
-
-impl Animate for ArcFlag {
-    #[inline]
-    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
-        (self.0 as i32)
-            .animate(&(other.0 as i32), procedure)
-            .map(|v| ArcFlag(v > 0))
-    }
-}
-
-impl ComputeSquaredDistance for ArcFlag {
-    #[inline]
-    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
-        (self.0 as i32).compute_squared_distance(&(other.0 as i32))
-    }
-}
-
-impl ToAnimatedZero for ArcFlag {
-    #[inline]
-    fn to_animated_zero(&self) -> Result<Self, ()> {
-        // The 2 ArcFlags in EllipticalArc determine which one of the 4 different arcs will be
-        // used. (i.e. From 4 combinations). In other words, if we change the flag, we get a
-        // different arc. Therefore, we return *self.
-        // https://svgwg.org/svg2-draft/paths.html#PathDataEllipticalArcCommands
-        Ok(*self)
-    }
-}
+pub type CoordPair = CoordinatePair<CSSFloat>;
 
 /// SVG Path parser.
 struct PathParser<'a> {
@@ -736,7 +517,7 @@ struct PathParser<'a> {
 macro_rules! parse_arguments {
     (
         $parser:ident,
-        $abs:ident,
+        $by_to:ident,
         $enum:ident,
         [ $para:ident => $func:ident $(, $other_para:ident => $other_func:ident)* ]
     ) => {
@@ -747,7 +528,9 @@ macro_rules! parse_arguments {
                     skip_comma_wsp(&mut $parser.chars);
                     let $other_para = $other_func(&mut $parser.chars)?;
                 )*
-                $parser.path.push(PathCommand::$enum { $para $(, $other_para)*, $abs });
+                $parser.path.push(
+                    PathCommand::$enum { $by_to, $para $(, $other_para)* }
+                );
 
                 // End of string or the next character is a possible new command.
                 if !skip_wsp(&mut $parser.chars) ||
@@ -785,23 +568,23 @@ impl<'a> PathParser<'a> {
             }
 
             let command = self.chars.next().unwrap();
-            let abs = if command.is_ascii_uppercase() {
-                IsAbsolute::Yes
+            let by_to = if command.is_ascii_uppercase() {
+                ByTo::To
             } else {
-                IsAbsolute::No
+                ByTo::By
             };
 
             skip_wsp(&mut self.chars);
             match command {
                 b'Z' | b'z' => self.parse_closepath(),
-                b'L' | b'l' => self.parse_lineto(abs),
-                b'H' | b'h' => self.parse_h_lineto(abs),
-                b'V' | b'v' => self.parse_v_lineto(abs),
-                b'C' | b'c' => self.parse_curveto(abs),
-                b'S' | b's' => self.parse_smooth_curveto(abs),
-                b'Q' | b'q' => self.parse_quadratic_bezier_curveto(abs),
-                b'T' | b't' => self.parse_smooth_quadratic_bezier_curveto(abs),
-                b'A' | b'a' => self.parse_elliptical_arc(abs),
+                b'L' | b'l' => self.parse_lineto(by_to),
+                b'H' | b'h' => self.parse_h_lineto(by_to),
+                b'V' | b'v' => self.parse_v_lineto(by_to),
+                b'C' | b'c' => self.parse_curveto(by_to),
+                b'S' | b's' => self.parse_smooth_curveto(by_to),
+                b'Q' | b'q' => self.parse_quadratic_bezier_curveto(by_to),
+                b'T' | b't' => self.parse_smooth_quadratic_bezier_curveto(by_to),
+                b'A' | b'a' => self.parse_elliptical_arc(by_to),
                 _ => return Err(()),
             }?;
         }
@@ -817,12 +600,8 @@ impl<'a> PathParser<'a> {
 
         skip_wsp(&mut self.chars);
         let point = parse_coord(&mut self.chars)?;
-        let absolute = if command == b'M' {
-            IsAbsolute::Yes
-        } else {
-            IsAbsolute::No
-        };
-        self.path.push(PathCommand::MoveTo { point, absolute });
+        let by_to = if command == b'M' { ByTo::To } else { ByTo::By };
+        self.path.push(PathCommand::Move { by_to, point });
 
         // End of string or the next character is a possible new command.
         if !skip_wsp(&mut self.chars) || self.chars.peek().map_or(true, |c| c.is_ascii_alphabetic())
@@ -833,69 +612,74 @@ impl<'a> PathParser<'a> {
 
         // If a moveto is followed by multiple pairs of coordinates, the subsequent
         // pairs are treated as implicit lineto commands.
-        self.parse_lineto(absolute)
+        self.parse_lineto(by_to)
     }
 
     /// Parse "closepath" command.
     fn parse_closepath(&mut self) -> Result<(), ()> {
-        self.path.push(PathCommand::ClosePath);
+        self.path.push(PathCommand::Close);
         Ok(())
     }
 
     /// Parse "lineto" command.
-    fn parse_lineto(&mut self, absolute: IsAbsolute) -> Result<(), ()> {
-        parse_arguments!(self, absolute, LineTo, [ point => parse_coord ])
+    fn parse_lineto(&mut self, by_to: ByTo) -> Result<(), ()> {
+        parse_arguments!(self, by_to, Line, [ point => parse_coord ])
     }
 
     /// Parse horizontal "lineto" command.
-    fn parse_h_lineto(&mut self, absolute: IsAbsolute) -> Result<(), ()> {
-        parse_arguments!(self, absolute, HorizontalLineTo, [ x => parse_number ])
+    fn parse_h_lineto(&mut self, by_to: ByTo) -> Result<(), ()> {
+        parse_arguments!(self, by_to, HLine, [ x => parse_number ])
     }
 
     /// Parse vertical "lineto" command.
-    fn parse_v_lineto(&mut self, absolute: IsAbsolute) -> Result<(), ()> {
-        parse_arguments!(self, absolute, VerticalLineTo, [ y => parse_number ])
+    fn parse_v_lineto(&mut self, by_to: ByTo) -> Result<(), ()> {
+        parse_arguments!(self, by_to, VLine, [ y => parse_number ])
     }
 
     /// Parse cubic Bézier curve command.
-    fn parse_curveto(&mut self, absolute: IsAbsolute) -> Result<(), ()> {
-        parse_arguments!(self, absolute, CurveTo, [
+    fn parse_curveto(&mut self, by_to: ByTo) -> Result<(), ()> {
+        parse_arguments!(self, by_to, CubicCurve, [
             control1 => parse_coord, control2 => parse_coord, point => parse_coord
         ])
     }
 
     /// Parse smooth "curveto" command.
-    fn parse_smooth_curveto(&mut self, absolute: IsAbsolute) -> Result<(), ()> {
-        parse_arguments!(self, absolute, SmoothCurveTo, [
+    fn parse_smooth_curveto(&mut self, by_to: ByTo) -> Result<(), ()> {
+        parse_arguments!(self, by_to, SmoothCubic, [
             control2 => parse_coord, point => parse_coord
         ])
     }
 
     /// Parse quadratic Bézier curve command.
-    fn parse_quadratic_bezier_curveto(&mut self, absolute: IsAbsolute) -> Result<(), ()> {
-        parse_arguments!(self, absolute, QuadBezierCurveTo, [
+    fn parse_quadratic_bezier_curveto(&mut self, by_to: ByTo) -> Result<(), ()> {
+        parse_arguments!(self, by_to, QuadCurve, [
             control1 => parse_coord, point => parse_coord
         ])
     }
 
     /// Parse smooth quadratic Bézier curveto command.
-    fn parse_smooth_quadratic_bezier_curveto(&mut self, absolute: IsAbsolute) -> Result<(), ()> {
-        parse_arguments!(self, absolute, SmoothQuadBezierCurveTo, [ point => parse_coord ])
+    fn parse_smooth_quadratic_bezier_curveto(&mut self, by_to: ByTo) -> Result<(), ()> {
+        parse_arguments!(self, by_to, SmoothQuad, [ point => parse_coord ])
     }
 
     /// Parse elliptical arc curve command.
-    fn parse_elliptical_arc(&mut self, absolute: IsAbsolute) -> Result<(), ()> {
+    fn parse_elliptical_arc(&mut self, by_to: ByTo) -> Result<(), ()> {
         // Parse a flag whose value is '0' or '1'; otherwise, return Err(()).
-        let parse_flag = |iter: &mut Peekable<Cloned<slice::Iter<u8>>>| match iter.next() {
-            Some(c) if c == b'0' || c == b'1' => Ok(ArcFlag(c == b'1')),
+        let parse_arc_size = |iter: &mut Peekable<Cloned<slice::Iter<u8>>>| match iter.next() {
+            Some(c) if c == b'1' => Ok(ArcSize::Large),
+            Some(c) if c == b'0' => Ok(ArcSize::Small),
+            _ => Err(()),
+        };
+        let parse_arc_sweep = |iter: &mut Peekable<Cloned<slice::Iter<u8>>>| match iter.next() {
+            Some(c) if c == b'1' => Ok(ArcSweep::Cw),
+            Some(c) if c == b'0' => Ok(ArcSweep::Ccw),
             _ => Err(()),
         };
-        parse_arguments!(self, absolute, EllipticalArc, [
-            rx => parse_number,
-            ry => parse_number,
-            angle => parse_number,
-            large_arc_flag => parse_flag,
-            sweep_flag => parse_flag,
+        parse_arguments!(self, by_to, Arc, [
+            radii => parse_coord,
+            rotate => parse_number,
+            arc_size => parse_arc_size,
+            arc_sweep => parse_arc_sweep,
             point => parse_coord
         ])
     }
diff --git a/servo/components/style/values/specified/text.rs b/servo/components/style/values/specified/text.rs
index 0e70bd26ac..e26a17ba27 100644
--- a/servo/components/style/values/specified/text.rs
+++ b/servo/components/style/values/specified/text.rs
@@ -454,7 +454,6 @@ pub enum TextAlignKeyword {
     Left,
     Right,
     Center,
-    #[cfg(any(feature = "gecko", feature = "servo-layout-2013"))]
     Justify,
     #[css(skip)]
     #[cfg(feature = "gecko")]
@@ -466,11 +465,11 @@ pub enum TextAlignKeyword {
     MozLeft,
     #[cfg(feature = "gecko")]
     MozRight,
-    #[cfg(feature = "servo-layout-2013")]
+    #[cfg(feature = "servo")]
     ServoCenter,
-    #[cfg(feature = "servo-layout-2013")]
+    #[cfg(feature = "servo")]
     ServoLeft,
-    #[cfg(feature = "servo-layout-2013")]
+    #[cfg(feature = "servo")]
     ServoRight,
 }
 
diff --git a/servo/components/style_traits/owned_slice.rs b/servo/components/style_traits/owned_slice.rs
index 36ba3162e5..c0d4ceff8d 100644
--- a/servo/components/style_traits/owned_slice.rs
+++ b/servo/components/style_traits/owned_slice.rs
@@ -13,7 +13,7 @@ use std::marker::PhantomData;
 use std::ops::{Deref, DerefMut};
 use std::ptr::NonNull;
 use std::{fmt, iter, mem, slice};
-use to_shmem::{self, SharedMemoryBuilder, ToShmem};
+use to_shmem::{SharedMemoryBuilder, ToShmem};
 
 /// A struct that basically replaces a `Box<[T]>`, but which cbindgen can
 /// understand.
diff --git a/servo/components/style_traits/values.rs b/servo/components/style_traits/values.rs
index 58b50d6576..e2154f606a 100644
--- a/servo/components/style_traits/values.rs
+++ b/servo/components/style_traits/values.rs
@@ -243,8 +243,9 @@ where
         Self { inner, separator }
     }
 
+    /// Serialize the CSS Value with the specific serialization function.
     #[inline]
-    fn write_item<F>(&mut self, f: F) -> fmt::Result
+    pub fn write_item<F>(&mut self, f: F) -> fmt::Result
     where
         F: FnOnce(&mut CssWriter<'b, W>) -> fmt::Result,
     {