WindowServer: Tweak look of window close button.

WindowServer/WSWindowManager.cpp

@@ -238,7 +238,7 @@ void WSWindowManager::paint_window_frame(WSWindow& window)
 
     m_back_painter->fill_rect_with_gradient(close_button_rect.shrunken(2, 2), Color::LightGray, Color::White);
 
-    m_back_painter->draw_rect(close_button_rect, Color::Black, true);
+    m_back_painter->draw_rect(close_button_rect, Color::DarkGray, true);
     auto x_location = close_button_rect.center();
     x_location.move_by(-(s_close_button_bitmap_width / 2), -(s_close_button_bitmap_height / 2));
     m_back_painter->draw_bitmap(x_location, *s_close_button_bitmap, Color::Black);