JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">

    <div id="aDiv">
        <p>some content</p>
    </div>

</div>

CSS

* {
    margin: 5;
    padding: 0;
    -webkit-box-sizing: border-box;
        -moz-box-sizing: border-box;
    box-sizing: border-box;
}

#container {
    width: 100%; height: 100%;
    background-color: red;
}

#aDiv {
    width: 100%;
    padding: 10%;
    background-color: blue;
}