.video-container {
  position: relative;
  padding-bottom: 56.25%; /* 16:9 の比率を維持 (9 / 16 = 0.5625) */
  height: 0;
  overflow: hidden;
  max-width: 100%;
}

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