html, body {
    height: 100%;
    width: 100%;
}

body {
    background-color: black;
    text-align: center;
    display: table;
}

main {
    margin: 0 auto;
    display: table-cell;
    vertical-align: middle;
}

@media only screen and (max-width: 853px) {

    main > iframe {
        width: 100%;
        height: 100%;

    }

    main {
        vertical-align: top;
    }
}