JSFiddle - React, Tailwind, and code Playground

HTML

<html>
<head>
</head>
<body>
  <div class="background" id="background"></div>
  <div class="page-content">Put your content here</div>
</body>
</html>

CSS

.background {
  background-color:whitesmoke;
  position:absolute;
  width:999em;
  height:999em;
  z-index:1;
}
.page-content {
  z-index:2;
  position:relative;
}

JavaScript

$(document).ready(function(){
  var windowHeight = $(window).height();
  var windowWidth = $(window).width();
  var animateWidth = '500'        
  $('#background').height(windowHeight).width(windowWidth)
     .animate({
        left: animateWidth + 'px',
        width: (windowWidth - animateWidth) + 'px'
      }, 2000);
});