JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

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

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

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

JavaScript

var test = document.getElementById('A'),
    test2 = document.getElementById('B');

test.onclick = function(){
  test2.classList.toggle('C');
}