win: allow dynamic switch dark mode

Zhao Yuhang

2023-12-22 e33059ee1ef7e1be07490ad0245676ded42589f4

 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;