JSFiddle - React, Tailwind, and code Playground

HTML

<div id="a">
	<div id="b"></div>
</div>
<div id="d"></div>

CSS

div {
	width: 50px;
	height: 50px;
    position: absolute;
    top: 15px;
    left: 5px;
}

#a {
    position: fixed;
	background-color: blue;
}
#b {
    /* should be on top according to spec */
	background-color: red;
    z-index: 400;
}
#d {
    /* on top in mobile webkit and chrome */
    background-color: yellow;
    left: 8px;
    top: 25px;
    z-index: 300;
}