in content/js/main.js [9:19]
$(window).scroll(function() {
// HTML5 proves useful for helping with creating JS functions!
// also, negative value because we're scrolling upwards
var yPos = -($window.scrollTop() / $scroll.data('speed'));
// background position
var coords = '50% '+ yPos + 'px';
// move the background
$scroll.css({ backgroundPosition: coords });
}); // end window scroll