JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
    width: 10px;
    height: 10px;
    background: black;
    box-shadow: 20px 0 0 black, 0 20px 0 black, 20px 20px 0 black, 10px 10px 0 black;
}