JSFiddle - React, Tailwind, and code Playground

HTML

<div id="header"></div>
<div id="container"></div>

CSS

html, body {
    margin:0;
    padding:0;
}
#header {
    width:100%;
    background:#d3d3d3;
    height:30px;
}
#container {
    width:80%;
    margin:0 auto;
    background:#939393;
    height:500px;
}