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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.btn {
  display: grid;
  place-items: center;
  width: 48px;
  height: 48px;
  border: 0;
  border-radius: 50%;
  background: rgba(255, 255, 255, 0.06);
  color: #00e5ff;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  box-shadow: 0 0 8px rgba(0, 229, 255, 0.3), 0 0 16px rgba(0, 229, 255, 0.12);
  transition: box-shadow 300ms ease-out, transform 300ms ease-out, background 300ms ease-out;
}

.btn:hover,
.btn:focus-visible {
  background: rgba(255, 255, 255, 0.1);
  box-shadow: 0 0 12px #00e5ff, 0 0 32px rgba(0, 229, 255, 0.65), 0 0 48px rgba(0, 229, 255, 0.3);
  transform: scale(1.06);
  outline: none;
}

.stage.is-demo .btn {
  animation: hover-loop 2s ease-out infinite;
}

@keyframes hover-loop {
  0%, 12%, 100% {
    box-shadow: 0 0 8px rgba(0, 229, 255, 0.3), 0 0 16px rgba(0, 229, 255, 0.12);
    transform: scale(1);
  }
  35%, 75% {
    box-shadow: 0 0 12px #00e5ff, 0 0 32px rgba(0, 229, 255, 0.65), 0 0 48px rgba(0, 229, 255, 0.3);
    transform: scale(1.06);
  }
  92% {
    box-shadow: 0 0 8px rgba(0, 229, 255, 0.3), 0 0 16px rgba(0, 229, 255, 0.12);
    transform: scale(1);
  }
}
@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .btn {
    animation: none;
  }
  .btn {
    transition-duration: 1ms;
  }
}