jellyfin-web/src/bower_components/emby-webcomponents/appfooter/appfooter.css

.appfooter {
    position: fixed;
    left: 0;
    right: 0;
    z-index: 1;
    bottom: 0;
    transition: transform 180ms linear;
    contain: layout style;
}

    .appfooter.headroom--unpinned {
        transform: translateY(100%)!important;
    }