JSFiddle - React, Tailwind, and code Playground

HTML

<body>
   <div class="parent"> /** Width:900px; **/
      <div class="inner"> /** This I want 100% of BODY, not of parent div **/

      </div>
   </div>
</body>

CSS

.parent {
background:red;
width:500px;
height:100px;
margin:0 auto;
}

.inner {
background:green;
height:100px;
position:absolute;
  left:0;
  right:0;
}