JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html>

<head>
</head>
	
<body>
		<div id="bottom">
				<div id="top"></div>
			</div>

</body>

</html>

CSS

#bottom {
  background: rgb(100,100,100);
  position: absolute;
  width: 300px;
  height: 300px;
}
#top {
  background: rgba(200, 0, 0, 0.2);
  position: absolute; 
  width: 100px; 
  height: 100px;
  top: 20px;
  left: 20px;
}