Made it possible to enable dark MacOS titlebar through the C definition MACOS_DARK_TITLEBAR

src/window_macos.m

@@ -2,6 +2,9 @@
 
 void macos_force_foreground_level() {
   [NSApp activateIgnoringOtherApps: YES];
+
+#ifdef MACOS_DARK_TITLEBAR
   // Set dark titlebar
-  // [[NSApplication sharedApplication].windows[0] setAppearance:[NSAppearance appearanceNamed:NSAppearanceNameVibrantDark]];
+  [[NSApplication sharedApplication].windows[0] setAppearance:[NSAppearance appearanceNamed:NSAppearanceNameVibrantDark]];
+#endif
 }