JSFiddle - React, Tailwind, and code Playground

HTML

<div id="s"></div>

CSS

#s {
	    position: relative;
	    width:200px;
	    height: 200px;
	    border-radius:8px;
	    background-color: red;
	    margin:0 auto;
	}
	#s:before {
	    content: '';
        z-index: -1;
	    background-color: green;
	    position: absolute;
	    top: -8px;
	    left: -8px;
        width: 216px;
        height: 216px;
}