/* カスタマイズ用CSS */
.youtube {
  position: relative;
  width: 100%;
  height: 0;
  padding-bottom: 56.25%;
  overflow: hidden;
  margin-bottom: 50px;
}
.youtube iframe {
  position: absolute;
  top: 0;
  right: 0;
  width: 100%;
  height: 100%;
}