JSFiddle - React, Tailwind, and code Playground

HTML

<div id="content">
    <div id="border"></div>
</div>

CSS

div#content {
    width: 200px;
    height: 200px;
    margin-left: 40px;
    margin-top: 40px;
    background-color: blue;
    position: relative;
}
div#border {
    position: relative;
    left: -20px;
    top: -20px;
    height: 240px;
    width: 40px;
    background-color: green;
    z-index: -1;
}