/*** for PC Browser ***/
@media (min-width:401px)
{
<style>
.video-container {
  width: 800px;
  height: 450px;
  margin: 0 auto;
  position: relative;
}
.video-container video {
  width: 100%;
  height: 100%;
  display: block;
  object-fit: cover;
}

}
@media screen and (max-width: 800px) {
  .video-container {
    width: 100%;
    height: auto;
    aspect-ratio: 16 / 9; /* 800:450 = 16:9 */
  }
  .video-container video {
    height: 100%;
  }
  @supports not (aspect-ratio: 1) {
    .video-container {
      height: 0;
      padding-top: 56.25%; /* 450/800=0.5625 → 56.25% */
      position: relative;
    }
    .video-container video {
      position: absolute;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
    }
  }
}
</style>