JSFiddle - React, Tailwind, and code Playground

HTML

<div class=bg></div>
<div class=box>blah</div>

CSS

html,body { min-height: 100%; }
body { background: yellow; }
.bg {
    position: fixed; top: 0; right: 0; bottom: 0; left: 0;
    background: blue;
}
.box {
    position: absolute; top: 5em; left: 50%; width: 20em; height: 200em; margin-left: -10em;
    background: red;
}