JSFiddle - React, Tailwind, and code Playground

HTML

<div id="Parent">
    <div id="Child">
        test content
    </div>
</div>

CSS

#Parent {
    width: 50px;
    height: 50px;
    border-width: 1px;
    border-style: solid;
}

#Child {
    position: relative;
    top: 30px;
    left: 30px;
    width: 50px;
    height: 50px;
    background: black;
    z-index: -1;
}