also adding on to other response, if the silly guy is getting cropped out change the numbers for bottom: and right: until it looks good!

nav::before {
  content: '';
  position: fixed;
  bottom: -150px;
  right: -100px;
  width: 400px;
  height: 400px;
  background-image: url(the-silly-guy);
  background-size: contain;
  background-repeat: no-repeat;
  z-index: 1000;
  pointer-events: none;
}

most people use body::before but that breaks the CRT effect you have