Test simple Parallax effect

HTML

<div id="top" class="bg"></div>
<div id="mid" class="bg"></div>
<div id="bottom" class="bg"></div>

CSS

.bg {
    position:absolute;
    top:0;
    left:0;
    right:0;
    bottom:0;
}
#top {
    z-index:1;
    background:url('http://placehold.it/350x350&text=theTopLayer');
}
#mid {
    z-index:2;
    background:url('http://placehold.it/100x100&text=theMidLayer');
    opacity:.5;
}
#bottom {
    z-index:3;
    background:url('http://placehold.it/350x350&text=theBottomLayer');
    opacity:.25;
}

JavaScript

function animateThis() {
    $('#top').css("background-position", "-=2");
    $('#mid').css("background-position", "-=8");
    $('#bottom').css("background-position", "-=12");
}

setInterval(animateThis, 100);