Dead simple background parallax scrolling in javascript.
(scroll up, down, left, and right)
<html>

    <head>

        <script>
        
            function onLoad() {
            
                window.onscroll = function() {
                    var speed = 8.0;
                    document.body.style.backgroundPosition = (-window.scrollX / speed) + "px " + (-window.scrollY / speed) + "px";
                }
            
            }
            
        </script>

    </head>

    <body onload="onLoad()">

    </body>

</html>

            
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