#wrap-video-bg{
  overflow: hidden;
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  z-index:-1;
  background: #000000;
}

#wrap-video-bg video{
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  object-fit: scale-down;
}

#bla{
  position: absolute;
  left: 50%;top: 50%;transform:translate(-50%,-50%);
  width: 100px;
  height: 100px;
  background: #000000;
}