Youtubeのレスポンシブ対応

.movieはiframeを囲うdivなど

.movie {
  position: relative;
  width: 100%;
  padding-top: 56.25%;
}
.movie iframe {
  position: absolute;
  top: 0;
  right: 0;
  width: 100% !important;
  height: 100% !important;
}