theme: derive elevations from the platform's native shadows

crates/theme/src/resolve.rs

@@ -220,7 +220,7 @@ pub(crate) fn resolve(
         },
         colors,
         radius,
-        elevations: Elevations::default(),
+        elevations: Elevations::for_platform(system.source, variant),
         motion: Motion::default(),
         scrollbar: Scrollbar::default(),
         root_font_size,
@@ -361,13 +361,42 @@ mod tests {
         );
 
         // The popover shadow is softer and tighter than the dialog's.
-        assert!(resolved.elevations.popover.blur_radius < resolved.elevations.dialog.blur_radius);
+        assert!(
+            resolved.elevations.popover.layers[0].blur_radius
+                < resolved.elevations.dialog.layers[0].blur_radius
+        );
         assert!(resolved.motion.overlay > std::time::Duration::ZERO);
         let shadows = resolved.elevations.popover.shadows();
         assert_eq!(shadows.len(), 1);
         assert!(!shadows[0].inset);
     }
 
+    #[test]
+    fn elevations_follow_the_platform_in_light_mode_and_share_one_dark_stack() {
+        let popover = |source| {
+            let mut stated = system(ThemeVariant::Light, PartialPalette::default(), None);
+            stated.source = source;
+            resolve(&stated, None, None).elevations.popover
+        };
+
+        // macOS paints a soft layered stack; Linux keeps a compact single one.
+        assert_eq!(popover(SourceKind::Macos).shadows().len(), 2);
+        assert_eq!(popover(SourceKind::Gnome).shadows().len(), 1);
+        assert!(
+            popover(SourceKind::Macos).layers[0].color.a
+                < popover(SourceKind::Gnome).layers[0].color.a
+        );
+
+        // Dark mode is one shared stack, however the adapter detected.
+        let dark = |source| {
+            let mut stated = system(ThemeVariant::Dark, PartialPalette::default(), None);
+            stated.source = source;
+            resolve(&stated, None, None).elevations
+        };
+        assert_eq!(dark(SourceKind::Macos), dark(SourceKind::Windows));
+        assert_eq!(dark(SourceKind::Macos), dark(SourceKind::Fallback));
+    }
+
     #[test]
     fn system_colors_override_the_base_but_leave_the_rest_intact() {
         let palette = PartialPalette {