JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
    border: 1px solid red;
    height: 22px;
    width: 22px;
}

.foo {
    height: 42px;
    width: 42px;
}

JavaScript

var div = document.querySelector('div');
div.classList.add('foo');
var style = window.getComputedStyle(div);
div.innerHTML = style['width'];