JSFiddle - React, Tailwind, and code Playground

HTML

<video id="moodvideo" autoplay loop>
    <source src="moodvideo.mp4" type='video/mp4'>
   <img id="alternative" src="alternative.jpg" />
</video>

CSS

#moodvideo, #alternative {
    width: 100vw;
    /* Could also use width: 100%; */
    height: 100vh;
    object-fit: cover;
    position: fixed;
    /* Change position to absolute if you don't want it to take up the whole page */
    left: 0px;
    top: 0px;
    z-index: -1;
}