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diff --git a/servo/components/style/values/computed/align.rs b/servo/components/style/values/computed/align.rs
new file mode 100644
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+++ b/servo/components/style/values/computed/align.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/. */
+
+//! Values for CSS Box Alignment properties
+//!
+//! https://drafts.csswg.org/css-align/
+
+use crate::values::computed::{Context, ToComputedValue};
+use crate::values::specified;
+
+pub use super::specified::{
+    AlignContent, AlignItems, AlignTracks, ContentDistribution, JustifyContent, JustifyTracks,
+    SelfAlignment,
+};
+pub use super::specified::{AlignSelf, JustifySelf};
+
+/// The computed value for the `justify-items` property.
+///
+/// Need to carry around both the specified and computed value to handle the
+/// special legacy keyword without destroying style sharing.
+///
+/// In particular, `justify-items` is a reset property, so we ought to be able
+/// to share its computed representation across elements as long as they match
+/// the same rules. Except that it's not true if the specified value for
+/// `justify-items` is `legacy` and the computed value of the parent has the
+/// `legacy` modifier.
+///
+/// So instead of computing `legacy` "normally" looking at get_parent_position(),
+/// marking it as uncacheable, we carry the specified value around and handle
+/// the special case in `StyleAdjuster` instead, only when the result of the
+/// computation would vary.
+///
+/// Note that we also need to special-case this property in matching.rs, in
+/// order to properly handle changes to the legacy keyword... This all kinda
+/// sucks :(.
+///
+/// See the discussion in https://bugzil.la/1384542.
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToCss, ToResolvedValue)]
+#[repr(C)]
+pub struct ComputedJustifyItems {
+    /// The specified value for the property. Can contain the bare `legacy`
+    /// keyword.
+    #[css(skip)]
+    pub specified: specified::JustifyItems,
+    /// The computed value for the property. Cannot contain the bare `legacy`
+    /// keyword, but note that it could contain it in combination with other
+    /// keywords like `left`, `right` or `center`.
+    pub computed: specified::JustifyItems,
+}
+
+pub use self::ComputedJustifyItems as JustifyItems;
+
+impl JustifyItems {
+    /// Returns the `legacy` value.
+    pub fn legacy() -> Self {
+        Self {
+            specified: specified::JustifyItems::legacy(),
+            computed: specified::JustifyItems::normal(),
+        }
+    }
+}
+
+impl ToComputedValue for specified::JustifyItems {
+    type ComputedValue = JustifyItems;
+
+    /// <https://drafts.csswg.org/css-align/#valdef-justify-items-legacy>
+    fn to_computed_value(&self, _context: &Context) -> JustifyItems {
+        use crate::values::specified::align;
+        let specified = *self;
+        let computed = if self.0 != align::AlignFlags::LEGACY {
+            *self
+        } else {
+            // If the inherited value of `justify-items` includes the
+            // `legacy` keyword, `legacy` computes to the inherited value, but
+            // we assume it computes to `normal`, and handle that special-case
+            // in StyleAdjuster.
+            Self::normal()
+        };
+
+        JustifyItems {
+            specified,
+            computed,
+        }
+    }
+
+    #[inline]
+    fn from_computed_value(computed: &JustifyItems) -> Self {
+        computed.specified
+    }
+}