QFD2/QFluentWidgets/qss/light/navigation_interface.qss

NavigationPanel[menu=true] {
    background-color: rgb(243, 243, 243);
    border: 1px solid rgb(229, 229, 229);
    border-top-right-radius: 7px;
    border-bottom-right-radius: 7px;
}

NavigationPanel[menu=false] {
    background-color: transparent;
    border: 1px solid transparent;
    border-top-right-radius: 7px;
    border-bottom-right-radius: 7px;
}

QScrollArea, #scrollWidget {
    border: none;
    background-color: transparent;
}

NavigationInterface {
    background-color: rgb(243, 243, 243);
}