citra/dist/qt_themes/default/style.qss

QPushButton#GraphicsAPIStatusBarButton {
    color: #656565;
    border: 1px solid transparent;
    background-color: transparent;
    padding: 0px 3px 0px 3px;
    text-align: center;
    min-width: 60px;
    min-height: 20px;
}

QPushButton#GraphicsAPIStatusBarButton:hover {
    border: 1px solid #76797C;
}

QPushButton#TogglableStatusBarButton {
    color: #959595;
    border: 1px solid transparent;
    background-color: transparent;
    padding: 0px 3px 0px 3px;
    text-align: center;
}

QPushButton#TogglableStatusBarButton:checked {
    color: #00FF00;
}

QPushButton#TogglableStatusBarButton:hover {
    border: 1px solid #76797C;
}

QPushButton#button_reset_defaults {
    min-width: 57px;
    padding: 4px 8px;
}