JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
    height:300px;
    width:100%;
    outline:thin solid black;
    position:relative;
    background:white;
}
div::after, div::before {
    height:300px;
    content:' ';
    position: absolute;
    top: 0;
    width: 33%;
}
div::after {
    right: 0;
    background-color: red;
}
div::before {
    left: 0;
    background-color: green;
}