JSFiddle - React, Tailwind, and code Playground

HTML

<video autoplay loop poster="polina.jpg" id="vid">
    <source src="http://clips.vorwaerts-gmbh.de/big_buck_bunny.webm" type="video/webm">
    <source src="http://clips.vorwaerts-gmbh.de/big_buck_bunny.mp4" type="video/mp4">
    </video>

CSS

video#vid {
position: fixed; right: 0; bottom: 0;
min-width: 100%; min-height: 100%;
width: auto; height: auto; z-index: -100;
background: url(polina.jpg) no-repeat;
background-size: cover;
margin: 0 auto;
}