JSFiddle - React, Tailwind, and code Playground

HTML

<div id="foo">bla test</div>

CSS

#foo {
	position: relative;
	width: 200px;
	height: 200px;
	background: green;
}
#foo::before {
	position: absolute; top: 0; left: 0;
	background: red;
	width: 24px;
	height: 24px;
}