JSFiddle - React, Tailwind, and code Playground

HTML

<div id='parent'>
    <div id='child'>
    </div>
</div>

CSS

#parent {
	width:50px;
	height:50px;
	background:red;
    position: relative;
}

#parent:after {
    background: red;
    content: "ON TOP";
    display: block;
    width: 100%;
    height: 100%;
    position: absolute;
    left: 0;
    top: 0;
    z-index: 1;
}

#child {
	width:50px;
	height:50px;
	background:blue;
}