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diff --git a/servo/components/style/values/generics/position.rs b/servo/components/style/values/generics/position.rs
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+/* 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/. */
+
+//! Generic types for CSS handling of specified and computed values of
+//! [`position`](https://drafts.csswg.org/css-backgrounds-3/#position)
+
+use crate::values::animated::ToAnimatedZero;
+use crate::values::generics::ratio::Ratio;
+
+/// A generic type for representing a CSS [position](https://drafts.csswg.org/css-values/#position).
+#[derive(
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    Deserialize,
+    MallocSizeOf,
+    PartialEq,
+    Serialize,
+    SpecifiedValueInfo,
+    ToAnimatedValue,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C)]
+pub struct GenericPosition<H, V> {
+    /// The horizontal component of position.
+    pub horizontal: H,
+    /// The vertical component of position.
+    pub vertical: V,
+}
+
+impl<H, V> PositionComponent for Position<H, V>
+where
+    H: PositionComponent,
+    V: PositionComponent,
+{
+    #[inline]
+    fn is_center(&self) -> bool {
+        self.horizontal.is_center() && self.vertical.is_center()
+    }
+}
+
+pub use self::GenericPosition as Position;
+
+impl<H, V> Position<H, V> {
+    /// Returns a new position.
+    pub fn new(horizontal: H, vertical: V) -> Self {
+        Self {
+            horizontal,
+            vertical,
+        }
+    }
+}
+
+/// Implements a method that checks if the position is centered.
+pub trait PositionComponent {
+    /// Returns if the position component is 50% or center.
+    /// For pixel lengths, it always returns false.
+    fn is_center(&self) -> bool;
+}
+
+/// A generic type for representing an `Auto | <position>`.
+/// This is used by <offset-anchor> for now.
+/// https://drafts.fxtf.org/motion-1/#offset-anchor-property
+#[derive(
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    Deserialize,
+    MallocSizeOf,
+    Parse,
+    PartialEq,
+    Serialize,
+    SpecifiedValueInfo,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C, u8)]
+pub enum GenericPositionOrAuto<Pos> {
+    /// The <position> value.
+    Position(Pos),
+    /// The keyword `auto`.
+    Auto,
+}
+
+pub use self::GenericPositionOrAuto as PositionOrAuto;
+
+impl<Pos> PositionOrAuto<Pos> {
+    /// Return `auto`.
+    #[inline]
+    pub fn auto() -> Self {
+        PositionOrAuto::Auto
+    }
+}
+
+/// A generic value for the `z-index` property.
+#[derive(
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    MallocSizeOf,
+    PartialEq,
+    Parse,
+    SpecifiedValueInfo,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C, u8)]
+pub enum GenericZIndex<I> {
+    /// An integer value.
+    Integer(I),
+    /// The keyword `auto`.
+    Auto,
+}
+
+pub use self::GenericZIndex as ZIndex;
+
+impl<Integer> ZIndex<Integer> {
+    /// Returns `auto`
+    #[inline]
+    pub fn auto() -> Self {
+        ZIndex::Auto
+    }
+
+    /// Returns whether `self` is `auto`.
+    #[inline]
+    pub fn is_auto(self) -> bool {
+        matches!(self, ZIndex::Auto)
+    }
+
+    /// Returns the integer value if it is an integer, or `auto`.
+    #[inline]
+    pub fn integer_or(self, auto: Integer) -> Integer {
+        match self {
+            ZIndex::Integer(n) => n,
+            ZIndex::Auto => auto,
+        }
+    }
+}
+
+/// Ratio or None.
+#[derive(
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C, u8)]
+pub enum PreferredRatio<N> {
+    /// Without specified ratio
+    #[css(skip)]
+    None,
+    /// With specified ratio
+    Ratio(
+        #[animation(field_bound)]
+        #[css(field_bound)]
+        #[distance(field_bound)]
+        Ratio<N>,
+    ),
+}
+
+/// A generic value for the `aspect-ratio` property, the value is `auto || <ratio>`.
+#[derive(
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C)]
+pub struct GenericAspectRatio<N> {
+    /// Specifiy auto or not.
+    #[animation(constant)]
+    #[css(represents_keyword)]
+    pub auto: bool,
+    /// The preferred aspect-ratio value.
+    #[animation(field_bound)]
+    #[css(field_bound)]
+    #[distance(field_bound)]
+    pub ratio: PreferredRatio<N>,
+}
+
+pub use self::GenericAspectRatio as AspectRatio;
+
+impl<N> AspectRatio<N> {
+    /// Returns `auto`
+    #[inline]
+    pub fn auto() -> Self {
+        AspectRatio {
+            auto: true,
+            ratio: PreferredRatio::None,
+        }
+    }
+}
+
+impl<N> ToAnimatedZero for AspectRatio<N> {
+    #[inline]
+    fn to_animated_zero(&self) -> Result<Self, ()> {
+        Err(())
+    }
+}