我怎样在HTML 5中将视频添加到网站背景？

<video autoplay muted loop id = "myVideo">   <source src = "demo.mp4" type = "video/mp4">   Your browser does not support HTML5 video.</video>

function display() {   if (video.paused) {      video.play();      btn.innerHTML = "Pause the video!";   } else {      video.pause();      btn.innerHTML = "Play";   }}