JSFiddle - React, Tailwind, and code Playground

HTML

<div class="A"></div>
<div class="B"></div>

CSS

.A{
	background-color:#C71114;
	width: 100px;
	height: 100px;
}

.B{
	background-color:#09E41B;
	width: 100px;
	height: 100px;
	transition: all 1s;
}

.C{
	background-color:#1E88DF;
	width: 100px;
	height: 100px;
	margin: 10px;
	transition: all 1s;
}

JavaScript

var test = document.querySelector('.A');
 
test.onclick = function(){
  var oElement = document.querySelector('.B');
  oElement.classList.toggle('C');
}