/* ============ 背景音乐控制器 ============ */
.bgm-control {
  position: fixed;
  left: 24px;
  bottom: 24px;
  z-index: 9999;
  display: flex;
  align-items: center;
  gap: 0;
  background: rgba(255,255,255,.95);
  border: 1px solid #e3e9f0;
  border-radius: 24px;
  padding: 6px;
  box-shadow: 0 4px 16px rgba(0,0,0,.1);
  transition: opacity .3s, padding .32s ease;
}
/* 展开态：鼠标悬停在控件上（或正在拖动滑杆）时显示音量调节，移开后自动收起 */
.bgm-control:hover,
.bgm-control.dragging { padding: 6px 12px 6px 6px; }
.bgm-control.hidden { opacity: 0; pointer-events: none; }

.bgm-play-btn {
  width: 36px; height: 36px;
  border-radius: 50%;
  background: #1e88e5;
  color: #fff;
  border: none;
  cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  padding: 0;
  flex-shrink: 0;
}
.bgm-play-btn:hover { background: #1565c0; }
.bgm-play-btn svg { width: 16px; height: 16px; }

.bgm-vol-wrap {
  display: flex;
  align-items: center;
  gap: 4px;
  /* 默认收起：不占宽度、不可交互，悬停控件时由 .bgm-control:hover 展开 */
  max-width: 0;
  margin-left: 0;
  opacity: 0;
  overflow: hidden;
  pointer-events: none;
  transition: max-width .32s ease, margin-left .32s ease, opacity .25s ease;
}
.bgm-control:hover .bgm-vol-wrap,
.bgm-control.dragging .bgm-vol-wrap {
  max-width: 132px;
  margin-left: 8px;
  opacity: 1;
  pointer-events: auto;
}
.bgm-vol-btn {
  width: 28px; height: 28px;
  border-radius: 50%;
  background: transparent;
  border: none;
  cursor: pointer;
  color: #6b7c8d;
  display: flex; align-items: center; justify-content: center;
  padding: 0;
}
.bgm-vol-btn:hover { color: #1e88e5; }
.bgm-vol-btn svg { width: 16px; height: 16px; }

.bgm-vol-slider {
  width: 80px;
  height: 4px;
  -webkit-appearance: none;
  appearance: none;
  background: #e3e9f0;
  border-radius: 2px;
  outline: none;
}
.bgm-vol-slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 14px; height: 14px;
  border-radius: 50%;
  background: #1e88e5;
  cursor: pointer;
  border: 2px solid #fff;
  box-shadow: 0 1px 3px rgba(0,0,0,.2);
}
.bgm-vol-slider::-moz-range-thumb {
  width: 14px; height: 14px;
  border-radius: 50%;
  background: #1e88e5;
  cursor: pointer;
  border: 2px solid #fff;
}

/* 播放中动画 */
.bgm-play-btn.playing .bars {
  display: inline-flex;
  gap: 2px;
  height: 14px;
  align-items: flex-end;
}
.bgm-play-btn.playing .bars span {
  width: 3px;
  background: #fff;
  border-radius: 2px;
  animation: bgmBar .9s ease-in-out infinite;
}
.bgm-play-btn.playing .bars span:nth-child(1) { animation-delay: 0s; }
.bgm-play-btn.playing .bars span:nth-child(2) { animation-delay: .15s; }
.bgm-play-btn.playing .bars span:nth-child(3) { animation-delay: .3s; }
.bgm-play-btn.playing .bars span:nth-child(4) { animation-delay: .45s; }
@keyframes bgmBar {
  0%, 100% { height: 3px; }
  50% { height: 14px; }
}
.bgm-play-btn:not(.playing) .bars { display: none; }
.bgm-play-btn:not(.playing) svg.icon-play { display: inline; }
.bgm-play-btn.playing svg.icon-play { display: none; }

@media (max-width: 480px) {
  .bgm-control,
  .bgm-control:hover,
  .bgm-control.dragging { left: 12px; bottom: 12px; padding: 4px; }
  /* 移动端始终只显示播放按钮（无鼠标悬停概念，避免展开后常驻遮挡） */
  .bgm-control:hover .bgm-vol-wrap,
  .bgm-control.dragging .bgm-vol-wrap { display: none; }
  .bgm-vol-slider { width: 50px; }
}