.ytube {
  display: block;
  margin-left: auto;
  margin-right: auto;
  padding-top: 56.25%;
  position: relative;
  width: 100%;
   iframe {
      height: 100%;
      left: 0;
      position: absolute;
      top: 0;
      width: 100%;
    }
    a {
      /* lityを動かすためにiframeを覆う */
      height: 100%;
      left: 0;
      position: absolute;
      top: 0;
      width: 100%;
    }
}