JSFiddle - React, Tailwind, and code Playground

HTML

<div></div><div></div>

CSS

div {
    position: relative;
    width: 500px;
    height: 200px;
    background-color: rgba(255, 0, 0, 0.5);
    margin-left: 200px;
}
div:first-child {
    position: fixed;
    width: 200px;
    background-color: rgba(0, 255, 0, 0.5);
    margin-left: 0;
    }