html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.panel {
  position: relative;
  overflow: hidden;
  width: clamp(200px, 70vw, 260px);
  height: clamp(120px, 42vw, 150px);
  border-radius: 16px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.panel__face {
  position: absolute;
  inset: 0;
  box-sizing: border-box;
  padding: clamp(12px, 5vw, 18px);
  text-align: left;
}

.panel__face--light {
  background: #fff7e6;
  color: #17141a;
  opacity: 1;
  animation: face-light 2s ease-out infinite;
}

.panel__face--dark {
  background: #17141a;
  color: #fff7e6;
  opacity: 0;
  animation: face-dark 2s ease-out infinite;
}

.panel__title {
  margin: 0 0 6px;
  font-weight: 700;
  font-size: clamp(12px, 3.6vw, 15px);
  line-height: 1.3;
  font-family: inherit;
}

.panel__line {
  margin: 0;
  width: 55%;
  height: 8px;
  border-radius: 4px;
  background: currentColor;
  opacity: 0.25;
}

.track {
  position: absolute;
  top: clamp(8px, 3vw, 12px);
  right: clamp(8px, 3vw, 12px);
  display: block;
  width: 44px;
  height: 24px;
  border-radius: 999px;
  overflow: hidden;
}

.track__bg {
  position: absolute;
  inset: 0;
}

.track__bg--light {
  background: rgba(255, 255, 255, 0.5);
  opacity: 1;
  animation: face-light 2s ease-out infinite;
}

.track__bg--dark {
  background: #17141a;
  opacity: 0;
  animation: face-dark 2s ease-out infinite;
}

.knob {
  position: absolute;
  top: 3px;
  left: 3px;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: #2f6df6;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  transform: translateX(0);
  animation: knob-slide 2s ease-out infinite;
}

@keyframes face-light {
  0%, 15% {
    opacity: 1;
  }
  40%, 60% {
    opacity: 0;
  }
  85%, 100% {
    opacity: 1;
  }
}
@keyframes face-dark {
  0%, 15% {
    opacity: 0;
  }
  40%, 60% {
    opacity: 1;
  }
  85%, 100% {
    opacity: 0;
  }
}
@keyframes knob-slide {
  0%, 15% {
    transform: translateX(0);
  }
  40%, 60% {
    transform: translateX(20px);
  }
  85%, 100% {
    transform: translateX(0);
  }
}
@media (prefers-reduced-motion: reduce) {
  .panel__face--light, .panel__face--dark, .track__bg--light, .track__bg--dark, .knob {
    animation: none !important;
  }
}