/* YouTube サムネール / プレーヤー (youtube.js) */
a.yt-embed,
iframe.yt-frame {
  display: block;
  width: 100%;
  max-width: 640px;
  aspect-ratio: 16 / 9;
  margin: 0.5em 0;
  border: 0;
  border-radius: 8px;
}
a.yt-embed {
  position: relative;
  overflow: hidden;
  background: #000;
}
a.yt-embed img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  margin: 0;
}
/* 再生ボタン */
a.yt-embed::after {
  content: "";
  position: absolute;
  inset: 0;
  margin: auto;
  width: 68px;
  height: 48px;
  border-radius: 12px;
  background: rgba(33, 33, 33, 0.8)
    url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 68 48'%3E%3Cpath d='M27 14v20l18-10z' fill='%23fff'/%3E%3C/svg%3E")
    center / contain no-repeat;
  transition: background-color 0.15s;
}
a.yt-embed:hover::after {
  background-color: #f00;
}