JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper">
<div id="block"></div>
</div>

CSS

#wrapper {
    width: 400px;
    height: 300px;
    background: url("https://dl.dropbox.com/u/2787908/background.png") no-repeat 0 0;
    position: relative;
    margin: 15px;
}

#block {
    width: 400px;
    height: 100px;
    background: #99f;
    position: absolute;
    top: 100px;
}

JavaScript

$(document).ready(function(){
    //$("#wrapper").animate({ backgroundPosition:"(0 -100px)" }, 20000, "linear");
    $("#block").animate({ top: 0 }, {
        duration: 20000,
        easing: "linear",
        step: function(now, fx){
            console.log("0 "+(parseInt($(this).css("top"), 10)-100)+"px");
            $("#wrapper").css("background-position", "0 "+(parseInt($(this).css("top"), 10)-99)+"px");
        }
    });
});




/* background position animation plugin */

(function($) {
    
    if(!document.defaultView || !document.defaultView.getComputedStyle){
        var oldCurCSS = jQuery.curCSS;
        jQuery.curCSS = function(elem, name, force){
            if(name === 'background-position'){
                name = 'backgroundPosition';
            }
            if(name !== 'backgroundPosition' || !elem.currentStyle || elem.currentStyle[ name ]){
                return oldCurCSS.apply(this, arguments);
            }
            var style = elem.style;
            if ( !force && style && style[ name ] ){
                return style[ name ];
            }
            return oldCurCSS(elem, 'backgroundPositionX', force) +' '+ oldCurCSS(elem, 'backgroundPositionY', force);
        };
    }
    
    var oldAnim = $.fn.animate;
    $.fn.animate = function(prop){
        if('background-position' in prop){
            prop.backgroundPosition = prop['background-position'];
            delete prop['background-position'];
        }
        if('backgroundPosition' in prop){
            prop.backgroundPosition = '('+ prop.backgroundPosition + ')';
        }
        return oldAnim.apply(this, arguments);
    };
    
    function toArray(strg){
        strg = strg.replace(/left|top/g,'0px');
        strg = strg.replace(/right|bottom/g,'100%');
        strg = strg.replace(/([0-9\.]+)(\s|\)|$)/g,"$1px$2");
        var res = strg.match(/(-?[0-9\.]+)(px|\%|em|pt)\s(-?[0-9\.]+)(px|\%|em|pt)/);
        return...