.video-block-opt {
  text-align: center;
  margin-bottom: 25px;
}

@media (max-width: 640px) {

  .video-block-opt {
    /*position: relative;*/
    padding-bottom: 56.25%;
    padding-top: 30px;
    height: 0;
    overflow: hidden;
  }

  .video-block-opt iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
  }
}