.theme {
    background-position: center;
    background-size: cover;
}

.theme.theme-default {
    background-image: url(https://i.imgur.com/OhYPBLc.jpeg);
}

.theme.theme-Nitzer {
    background-image: url(https://i.imgur.com/Oaqsgms.jpeg);
}

.theme.theme-Depeche {
    background-image: url(https://i.imgur.com/YgOCZ9T.jpeg);
}

.theme.theme-Pink {
    background-image: url(https://i.imgur.com/sUNy2oU.jpeg);
}

.theme.theme-Poizon {
    background-image: url(https://i.imgur.com/OI0EMMd.jpeg);
}

.theme.theme-Cyber {
    background-image: url(https://i.imgur.com/z3dfx2r.jpeg);
}