mainwindowStyle.qss

* {
    background-color: rgb(40, 40, 58);
    color: white;
}
QPushButton {
    background-color: rgb(40, 40, 55);
    border-style: outset;
    border-width: 2px;
    border-radius: 4px;
    border-color: rgb(80, 80, 100);
    padding: 2px;
}
QPushButton:pressed {
    border-style: outset;
    background-color: rgb(100, 100, 140);
}