JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    Hello
    <span></span>
</div>

CSS

div {
   position: relative; 
}

div:after {
    content: "";
    position: absolute;
    width: 100%;
    height: 100%;
    background: #f00;
    z-index: -1;
    left: 0;
    top: 0;
}