jellyfin-web/dashboard-ui/themes/android.css

.viewMenuBar, .libraryViewNav {
    background-color: #191919;
}

.ui-page-theme-b {
    background-color: #292929;
}

.backdropPage.ui-page-theme-b {
    background-color: rgba(20, 20,20, .94) !important;
}

.defaultBackground .cardImage {
    background-color: #383838;
}