JSFiddle - React, Tailwind, and code Playground

HTML

<div class="height"></div>

CSS

.height {
  display: block;
  width: 30px;
  height: 30px;
  background: #cecece;
  animation: height  1s infinite linear;
}
@keyframes height {
  from {height: 30px}
  to {height: 0}
}

JavaScript

document.addEventListener("click", function(event) {
	console.log('start');
  var i = 5000000000;
  while(i >= 0){
			i--;
	}
	console.log('end'); 
});