JSFiddle - React, Tailwind, and code Playground

HTML

<div id="div1">
  <div id="div2"></div>
</div>

CSS

body, html {
  height: 100%;
  margin: 0;
}

div {
  width: 100%;
  display: block;
}

#div1 {
  height: 100%;
  background-color: lightgrey;
}

#div2 {
  background-color: red;
}