JSFiddle - React, Tailwind, and code Playground

HTML

<div ID="FIXED" onclick="this.style.display = 'none'" >
  <div ID="CONTENT" onclick="this.style.display = 'none'">
  </div>
</div>

CSS

#FIXED
{
  position:fixed;
  width:100%;
  height:100%;
  background-color:black;
  
}
#CONTENT
{
  position:relative;
  width:400px;
  height:400px;
  color:white;
  background-color:white;
  left: 50%;
	top: 50%;
	transform: translate(-50%, -50%);
}