JSFiddle - React, Tailwind, and code Playground

HTML

<div class="backgroundimagewrapper">
        <img class="backgroundimage" src="http://i.stack.imgur.com/qi2jc.png" />
    </div>
<h1>This appears on top!</h1>
<p>Amazing!</p>

CSS

.backgroundimagewrapper{
        position: absolute; /* So we can position our div precisely */
        left: 0; /* Move it to the top-left */
        top: 0;
        z-index: -100; /* Make it appear behind other elements */
        padding: 0; /* Make sure we don't have any white space around the edges */
        margin: 0;
        width: 100%; /* Make it fill our whole screen */
        height: 100%;
    }
    .backgroundimage{
        width: 100%; /* Make the image fill the whole div */
        height: 100%;
     }