/* Nút nhạc nền (E14): góc dưới phải của thẻ thiệp */
.music {
  position: fixed;
  right: max(16px, calc(50% - var(--card) / 2 + 16px));
  bottom: calc(18px + env(safe-area-inset-bottom, 0px));
  z-index: 40;
  display: grid; place-items: center;
  width: 46px; height: 46px; padding: 0;
  border: 1px solid rgba(5, 75, 38, .35); border-radius: 50%;
  background: rgba(247, 245, 239, .92); color: var(--green);
  box-shadow: 0 6px 18px rgba(0, 0, 0, .18);
  -webkit-backdrop-filter: blur(6px); backdrop-filter: blur(6px);
  cursor: pointer;
}
.music[hidden] { display: none; }
.music__icon { width: 22px; height: 22px; fill: currentColor; }
.music.is-playing .music__icon { animation: spin 4s linear infinite; }
.music__slash { position: absolute; width: 26px; height: 1.6px; border-radius: 2px; background: currentColor; transform: rotate(-45deg); }
.music.is-playing .music__slash { display: none; }
@keyframes spin { to { transform: rotate(360deg); } }