jellyfin-web/dashboard-ui/css/librarybrowser.css

/*.libraryContent {
}

.librarySidebar {
    display: none;
}

@media all and (min-width: 650px) {

    .libraryContent {
        float: right;
        width: 65%;
    }

    .librarySidebar {
        display: block;
        position: fixed;
        top: 0;
        left: 0;
        bottom: 0;
        width: 35%;
        border-right: 2px solid #666;
    }
}

@media all and (min-width: 750px) {
    .libraryContent {
        width: 70%;
    }

    .librarySidebar {
        width: 30%;
    }
}

@media all and (min-width: 1200px) {
    .libraryContent {
        width: 75%;
    }

    .librarySidebar {
        width: 25%;
    }
}

@media all and (min-width: 1440px) {
    .libraryContent {
        width: 80%;
    }

    .librarySidebar {
        width: 20%;
    }
}

@media all and (min-width: 1920px) {
    .libraryContent {
        width: 87.5%;
    }

    .librarySidebar {
        width: 12.5%;
    }
}*/