JSFiddle - React, Tailwind, and code Playground

HTML

<div class='parent'>
  <div class='child'>
  
  </div>
</div>

CSS

.parent {
  height:100px;
  width:100px;
  background-color: blue;
}

.child {
  height:10%;
  width:100%;
  background-color: red;
}