#kai-video,
#yidong-kai {
  position: fixed;
  top: 0;
  left: 0;
  z-index: 9999;

  width: 100%;
  height: 100%;
}

#kai-video video,
#yidong-kai img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

@media (min-width: 999px) {
  #yidong-kai {
    display: none;
  }
}
@media (max-width: 999px) {
  #kai-video {
    display: none;
  }
}