Update .multimedia to aspect-ratio with @supports fallback

[nerdpruitt]

Something to this effect:

.multimedia {
    aspect-ratio: 16 / 9;
}

@supports not (aspect-ratio: 16 / 9) {
    .multimedia {
        position: relative;
        width: 100%;
    }

    .multimedia::before {
        content: '';
        display: block;
        height: 0;
        padding-bottom: 56.25%;
    }
}