Optimize system button area APIs

SineStriker

2023-12-29 76924a335f40a0c3cc13805b4cb9429c336d33ca

 examples/mainwindow/light-style.qss

@@ -144,6 +144,10 @@
    background-color: #F3F3F3;
}

MainWindow[custom-style=true] {
    background-color: transparent;
}

QWidget#clock-widget {
    font-size: 75px;
    color: #333333;