Bug 1704016: Stop overriding NSWindow appearance with Dark Aqua, to ensure proper contrast between text and background in sheet windows. r=mstange

The sheet window background always follows the sheetParent window's appearance. So we can only use the dark appearance if child sheet contents use text colors that are compatible with the dark appearance. But at the moment, sheet documents always use the Light ColorScheme for their system colors, resulting in black-on-dark text.

Differential Revision: https://phabricator.services.mozilla.com/D111415

widget/cocoa/nsCocoaWindow.mm

@@ -3227,9 +3227,15 @@ static const NSString* kStateWantsTitleDrawn = @"wantsTitleDrawn";
       case nsIWidget::WindowAppearance::eLight:
         self.appearance = [NSAppearance appearanceNamed:NSAppearanceNameAqua];
         break;
-      case nsIWidget::WindowAppearance::eDark:
+      // eDark is currently disabled.
+      // The sheet window background always follows the sheetParent window's
+      // appearance. So we can only use the dark appearance if child sheet
+      // contents use text colors that are compatible with the dark appearance.
+      // But at the moment, sheet documents always use the Light ColorScheme for
+      // their system colors, resulting in black-on-dark text. See bug 1704016.
+      /*case nsIWidget::WindowAppearance::eDark:
         self.appearance = [NSAppearance appearanceNamed:NSAppearanceNameDarkAqua];
-        break;
+        break;*/
       default:
         // nil means "inherit effectiveAppearance from self.appearanceSource".
         self.appearance = nil;