Full video background how does it work?

Question

PHP

I can not understand. Here is the script on codepen
The css says

@media screen and (max-device-width: 800px) {
  html { background: url(//demosthenes.info/assets/images/polina.jpg) #000 no-repeat center center fixed; }
  #bgvid { display: none; }
}

But if you reduce the screen, the video does not disappear. Is it just me or everyone? And why?

Answer 1

And why should it disappear if the general rules for the video tag are set?

video { 
    position: fixed;
    top: 50%;
    left: 50%;
    min-width: 100%;
    min-height: 100%;
...

Answer 2

change (max-device-width: 800px) to (max-width: 800px)