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";
   }
}