fix: keep macOS main window titlebar opaque

src/gui/application/gui_application.cpp

@@ -2007,7 +2007,7 @@ void GuiApplication::SyncMainWindow() {
   }
 #if defined(__APPLE__)
   if (ui_->main_native_titlebar_attempts > 0) {
-    if (HideDisabledMainWindowZoomButton()) {
+    if (ConfigureMainWindowTitlebar()) {
       ui_->main_native_titlebar_attempts = 0;
     } else {
       --ui_->main_native_titlebar_attempts;

src/gui/platform/window_drag.h

@@ -8,9 +8,10 @@ namespace crossdesk {
 // left-mouse-down event. Returns false when no suitable native event exists.
 bool StartNativeWindowDrag();
 
-// Hides the disabled native zoom button on CrossDesk's fixed-size main
+// Normalizes the native title bar and hides the disabled zoom button on
-// window. Returns true once the matching AppKit window has been configured.
+// CrossDesk's fixed-size main window. Returns true once the matching AppKit
-bool HideDisabledMainWindowZoomButton();
+// window has been configured.
+bool ConfigureMainWindowTitlebar();
 
 // Configures live resize and replaces the stream window's native Space
 // fullscreen action with an immediate, single-window fullscreen transition.

src/gui/platform/window_drag_mac.mm

@@ -79,7 +79,7 @@ bool StartNativeWindowDrag() {
   }
 }
 
-bool HideDisabledMainWindowZoomButton() {
+bool ConfigureMainWindowTitlebar() {
   @autoreleasepool {
     for (NSWindow *window in [NSApp windows]) {
       if (![window.title isEqualToString:@"CrossDesk"]) {
@@ -94,6 +94,17 @@ bool HideDisabledMainWindowZoomButton() {
         continue;
       }
 
+      // Slint creates its winit windows with transparency enabled. That makes
+      // the native title-bar material depend on the SDK used to build the
+      // Slint runtime. The main window paints an opaque white surface, so make
+      // the corresponding AppKit window opaque as well and explicitly retain
+      // the standard, non-overlay title bar.
+      window.styleMask =
+          window.styleMask & ~NSWindowStyleMaskFullSizeContentView;
+      window.titleVisibility = NSWindowTitleVisible;
+      window.titlebarAppearsTransparent = NO;
+      window.backgroundColor = NSColor.whiteColor;
+      window.opaque = YES;
       zoom_button.hidden = YES;
       return true;
     }