JSFiddle - React, Tailwind, and code Playground

HTML

<div class='el1'>

</div>
<div class='el2'>

</div>

CSS

body{
  font-size: 16px;
}

.el1{
  font-size: 1em;
  width: 20em;
  height: 4em;
  background-color: green;
}

.el2{
  font-size: 0.5em;
  width: 20em;
  height: 4em;
  background-color: blue;
}