Match the macOS app appearance to the selected theme

crates/gpui/src/app.rs

@@ -1325,6 +1325,20 @@ impl App {
         self.platform.window_appearance()
     }
 
+    /// Overrides the appearance (light/dark) applied to the app's windows, independent of
+    /// the OS-wide setting. Pass `None` to clear the override and follow the system again.
+    /// The current value is reported by [`App::window_appearance`].
+    ///
+    /// On macOS this sets the underlying `NSApplication.appearance`, which controls the
+    /// native window chrome (the window border and titlebar) of every window. Use this
+    /// when the app uses a dark theme while the system is in light mode (or vice versa)
+    /// so the window edges render to match the theme. While an appearance is forced,
+    /// windows stop tracking system light/dark changes; pass `None` to resume following
+    /// the system. On other platforms this is a no-op.
+    pub fn set_window_appearance(&self, appearance: Option<WindowAppearance>) {
+        self.platform.set_window_appearance(appearance);
+    }
+
     /// Returns the window button layout configuration when supported.
     pub fn button_layout(&self) -> Option<WindowButtonLayout> {
         self.platform.button_layout()

crates/gpui/src/platform.rs

@@ -167,6 +167,16 @@ pub trait Platform: 'static {
     /// Returns the appearance of the application's windows.
     fn window_appearance(&self) -> WindowAppearance;
 
+    /// Overrides the appearance (light/dark) applied to the app's windows, independent
+    /// of the OS-wide setting. Pass `None` to clear the override and follow the system
+    /// again. The override is reflected by [`Platform::window_appearance`].
+    ///
+    /// Currently only implemented on macOS, where it sets `NSApplication.appearance` so
+    /// the native window chrome (the window border and titlebar) of every window matches
+    /// a dark app theme even when the system is in light mode (or vice versa). A no-op on
+    /// other platforms.
+    fn set_window_appearance(&self, _appearance: Option<WindowAppearance>) {}
+
     /// Returns the window button layout configuration when supported.
     fn button_layout(&self) -> Option<WindowButtonLayout> {
         None

crates/gpui_macos/src/platform.rs

@@ -7,9 +7,10 @@ use anyhow::{Context as _, anyhow};
 use block::ConcreteBlock;
 use cocoa::{
     appkit::{
-        NSApplication, NSApplicationActivationPolicy::NSApplicationActivationPolicyRegular,
-        NSControl as _, NSEventModifierFlags, NSMenu, NSMenuItem, NSModalResponse, NSOpenPanel,
-        NSSavePanel, NSVisualEffectState, NSVisualEffectView, NSWindow,
+        NSAppearanceNameVibrantDark, NSAppearanceNameVibrantLight, NSApplication,
+        NSApplicationActivationPolicy::NSApplicationActivationPolicyRegular, NSControl as _,
+        NSEventModifierFlags, NSMenu, NSMenuItem, NSModalResponse, NSOpenPanel, NSSavePanel,
+        NSVisualEffectState, NSVisualEffectView, NSWindow,
     },
     base::{BOOL, NO, YES, id, nil, selector},
     foundation::{
@@ -675,6 +676,29 @@ impl Platform for MacPlatform {
         }
     }
 
+    fn set_window_appearance(&self, appearance: Option<WindowAppearance>) {
+        unsafe {
+            let app: id = msg_send![APP_CLASS, sharedApplication];
+            // `None` clears the override by setting a nil appearance, so the app
+            // falls back to tracking the system-wide light/dark setting.
+            let ns_appearance: id = match appearance {
+                None => nil,
+                Some(appearance) => {
+                    let name: id = match appearance {
+                        WindowAppearance::Light => crate::window_appearance::NSAppearanceNameAqua,
+                        WindowAppearance::Dark => {
+                            crate::window_appearance::NSAppearanceNameDarkAqua
+                        }
+                        WindowAppearance::VibrantLight => NSAppearanceNameVibrantLight,
+                        WindowAppearance::VibrantDark => NSAppearanceNameVibrantDark,
+                    };
+                    msg_send![class!(NSAppearance), appearanceNamed: name]
+                }
+            };
+            let _: () = msg_send![app, setAppearance: ns_appearance];
+        }
+    }
+
     fn open_url(&self, url: &str) {
         unsafe {
             let ns_url = NSURL::alloc(nil).initWithString_(ns_string(url));

crates/zed/src/zed.rs

@@ -436,6 +436,7 @@ pub fn initialize_workspace(app_state: Arc<AppState>, cx: &mut App) {
     .detach();
 
     init_cursor_hide_mode(cx);
+    init_app_appearance(cx);
     init_reduce_motion(cx);
 
     cx.observe_new(|_multi_workspace: &mut MultiWorkspace, window, cx| {
@@ -2019,6 +2020,24 @@ fn init_cursor_hide_mode(cx: &mut App) {
     cx.observe_global::<SettingsStore>(apply).detach();
 }
 
+fn init_app_appearance(cx: &mut App) {
+    // Force the native window chrome (border + titlebar) to match the selected theme.
+    // `System` follows the OS (no override); any other theme forces its appearance, so a
+    // dark theme doesn't render a light window border when the system is in light mode.
+    let apply = |cx: &mut App| {
+        let appearance = match ThemeSettings::get_global(cx).theme.mode() {
+            Some(theme_settings::ThemeAppearanceMode::System) => None,
+            _ => Some(match cx.theme().appearance() {
+                theme::Appearance::Light => gpui::WindowAppearance::Light,
+                theme::Appearance::Dark => gpui::WindowAppearance::Dark,
+            }),
+        };
+        cx.set_window_appearance(appearance);
+    };
+    apply(cx);
+    cx.observe_global::<SettingsStore>(apply).detach();
+}
+
 #[derive(Copy, Clone, Debug, settings::RegisterSetting)]
 struct ReduceMotionSetting(settings::ReduceMotionMode);