Creating a fullscreen HTML5 video background with CSS – Slicejack

.fullscreen-bg { position: fixed; top: 0; right: 0; bottom: 0; left: 0; overflow: hidden; z-index: -100;}.fullscreen-bg__video { position: absolute; top: 0; left: 0; width: 100%; height: 100%;}

Source: Creating a fullscreen HTML5 video background with CSS – Slicejack