improve dark mode on win

Zhao Yuhang

2023-12-22 e331fb1feda8891baba2a2dc1caeed67834d9d93

 src/widgets/widgetwindowagent.h

@@ -26,6 +26,7 @@
        QWidget *systemButton(SystemButton button) const;
        void setSystemButton(SystemButton button, QWidget *w);

        // Not implement, don't use now
#ifdef Q_OS_MAC
        QWidget *systemButtonArea() const;
        void setSystemButtonArea(QWidget *widget);