JSFiddle - React, Tailwind, and code Playground

HTML

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

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

CSS

.A{
	width:50px;
	height:50px;
	background-color:#000000;
}

.B{
	width:100px;
	height:100px;
	background-color:#FF0004;
}

.C{
	width:150px;
	height:150px;
	background-color:#12FF00;
}

JavaScript

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

test.onclick = function(){
  test2.document.GetElementsByclassName('C');
}