JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div:before{
content: "";
display: block;    
width: 50px;
height: 50px;
background: red;    
}
div.class:before{
background: blue;
content: ' ';    
}

JavaScript

$('div').click(function(){
    $(this).addClass('class');
});