JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
  <div class="child">
        test child
  </div>
</div>

CSS

body{
  background:gray;  
  font-size:2rem;
  padding:2rem;
}
.parent{
  border:4px solid red;
}
.child{
  padding:2rem;
  background:lightyellow;
  width:100%;
}