JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div class="child">Something</div>
    <div class="child behind_parent">Something else</div>
    <div class="child">Something else entirely</div>
    <div id="parent"></div>
</div>

CSS

#container {
    position: fixed;
    padding: 10px;
}

#parent {
    background: orange;
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    z-index: 1;
}

.child {
    position: relative;
    background: red;
    margin: 5px 5px;
    z-index: 2;
}

.behind_parent {
    z-index: 0;   
}