*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --bg: #0f0f0f;
  --surface: #1a1a1a;
  --border: rgba(255, 255, 255, 0.08);
  --text: #ffffff;
  --muted: rgba(255, 255, 255, 0.45);
  --accent: #ff6b35;
}

html, body {
  height: 100%;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
  -webkit-tap-highlight-color: transparent;
  touch-action: manipulation;
  user-select: none;
  overflow: hidden;
}

.back-link {
  position: fixed;
  top: 1.2rem;
  left: 1.5rem;
  font-size: 0.65rem;
  font-weight: 600;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--muted);
  text-decoration: none;
  transition: color 0.2s ease;
  z-index: 10;
}

.back-link:hover {
  color: var(--text);
}

#install-btn {
  position: fixed;
  top: 1.2rem;
  right: 1.5rem;
  background: transparent;
  border: none;
  cursor: pointer;
  font-size: 0.65rem;
  font-weight: 600;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--muted);
  padding: 0;
  z-index: 10;
  transition: color 0.2s ease;
  -webkit-tap-highlight-color: transparent;
}

#install-btn:hover {
  color: var(--text);
}

#app {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 100%;
  gap: 2.5rem;
  padding: 2rem;
}

.noise-type-label {
  font-size: 0.7rem;
  font-weight: 600;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--muted);
  height: 1em;
  transition: color 0.3s ease;
}

.noise-type-label.playing {
  color: var(--accent);
}

.noise-btns {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
  justify-content: center;
}

.noise-btn {
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--text);
  font-family: inherit;
  font-size: 1.1rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  width: 7rem;
  height: 7rem;
  border-radius: 1rem;
  cursor: pointer;
  transition: background 0.15s ease, border-color 0.15s ease, color 0.15s ease, transform 0.1s ease;
  -webkit-tap-highlight-color: transparent;
}

.noise-btn:active {
  transform: scale(0.95);
}

.noise-btn.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #0f0f0f;
}

.noise-btn:not(.active):hover {
  border-color: rgba(255, 255, 255, 0.2);
  background: rgba(255, 255, 255, 0.05);
}

.volume-row {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  width: min(20rem, 100%);
}

.vol-icon {
  font-size: 0.75rem;
  color: var(--muted);
  flex-shrink: 0;
}

#volume {
  -webkit-appearance: none;
  appearance: none;
  flex: 1;
  height: 3px;
  background: var(--border);
  border-radius: 2px;
  outline: none;
  cursor: pointer;
}

#volume::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 1.1rem;
  height: 1.1rem;
  border-radius: 50%;
  background: var(--accent);
  cursor: pointer;
}

#volume::-moz-range-thumb {
  width: 1.1rem;
  height: 1.1rem;
  border-radius: 50%;
  background: var(--accent);
  border: none;
  cursor: pointer;
}

.pulse-ring {
  width: 6rem;
  height: 6rem;
  border-radius: 50%;
  border: 2px solid var(--accent);
  opacity: 0;
  pointer-events: none;
}

.pulse-ring.active {
  animation: pulse 2s ease-out infinite;
}

@keyframes pulse {
  0% { transform: scale(0.8); opacity: 0.5; }
  70% { transform: scale(1.4); opacity: 0; }
  100% { transform: scale(1.4); opacity: 0; }
}