1 files changed, 28 insertions, 13 deletions

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.