JSFiddle - React, Tailwind, and code Playground

HTML

<div onclick="doSomething()" id="parent">
    <div id="child"></div>
</div>

CSS

#parent {
    background-color: blue;
    width: 100%;
    height: 100px;
}

#child {
    background-color: green;
    width: 50%;
    height: inherit;
}

.myClass {
    background-color: red !important;
}

JavaScript

function doSomething() {
	event.target.className = ('myClass');
}