JSFiddle - React, Tailwind, and code Playground

HTML

<div id="outer">OUTER
    <div id="inner">INNER</div>
</div>

CSS

#outer {
        height: 100%;
        width: 100%;
        padding:5px;
        background-color: yellow;
        box-sizing:border-box;
    }
    #inner {
        height: 100%;
        width: 100%;
        background-color: blue;
        box-sizing:border-box;
    }