CSS - Background-size: cover

Question

$dkn-cover: 'img.jpg';
.background-size {
    // no-repeat comes first
    background: url($dkn-cover) no-repeat fixed;
    
    // followed by cover
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
}