:root {
  --bg: #0f172a;
  --panel: #1e293b;
  --panel-light: #334155;
  --text: #f8fafc;
  --text-muted: #94a3b8;
  --accent: #22d3ee;
  --accent-hover: #67e8f9;
  --danger: #f43f5e;
  --shadow: 0 10px 30px rgba(0, 0, 0, 0.35);
}

* {
  box-sizing: border-box;
}

html, body {
  margin: 0;
  padding: 0;
}

body {
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: radial-gradient(circle at top, #1e293b 0%, #0f172a 100%);
  color: var(--text);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 1.5rem;
}

.container {
  width: 100%;
  max-width: 640px;
  background: var(--panel);
  border-radius: 24px;
  box-shadow: var(--shadow);
  overflow: hidden;
}

header {
  padding: 2rem 2rem 1rem;
  text-align: center;
  background: linear-gradient(135deg, #0ea5e9 0%, var(--accent) 100%);
}

header h1 {
  margin: 0;
  font-size: 1.75rem;
  font-weight: 700;
}

header p {
  margin: 0.5rem 0 0;
  opacity: 0.9;
  font-size: 0.95rem;
}

main {
  padding: 1.5rem 2rem 2rem;
}

.display {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1.5rem;
  margin-bottom: 1.5rem;
}

.frequency-readout {
  font-variant-numeric: tabular-nums;
  font-size: 3.5rem;
  font-weight: 800;
  line-height: 1;
  color: var(--accent);
}

.frequency-readout .unit {
  font-size: 1.5rem;
  font-weight: 500;
  color: var(--text-muted);
  margin-left: 0.25rem;
}

.play-button {
  width: 72px;
  height: 72px;
  border-radius: 50%;
  border: none;
  background: var(--accent);
  color: var(--bg);
  font-size: 1.75rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background 0.15s ease, transform 0.1s ease;
  box-shadow: 0 4px 15px rgba(34, 211, 238, 0.35);
}

.play-button:hover {
  background: var(--accent-hover);
}

.play-button:active {
  transform: scale(0.95);
}

.play-button.playing {
  background: var(--danger);
  box-shadow: 0 4px 15px rgba(244, 63, 94, 0.35);
}

.play-button.playing:hover {
  background: #fb7185;
}

.stop-icon {
  display: none;
}

.play-button.playing .play-icon {
  display: none;
}

.play-button.playing .stop-icon {
  display: inline;
}

.controls {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.control-group {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.control-group label,
.presets label {
  font-size: 0.85rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
}

input[type="range"] {
  width: 100%;
  accent-color: var(--accent);
  cursor: pointer;
}

input[type="number"],
select {
  background: var(--panel-light);
  border: 1px solid #475569;
  border-radius: 10px;
  padding: 0.65rem 0.85rem;
  color: var(--text);
  font-size: 1rem;
}

input[type="number"]:focus,
select:focus {
  outline: none;
  border-color: var(--accent);
}

select {
  cursor: pointer;
}

.freq-inputs {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.freq-inputs input {
  flex: 1;
}

.hz-label {
  color: var(--text-muted);
  font-weight: 500;
}

.value-label {
  text-align: right;
  font-variant-numeric: tabular-nums;
  color: var(--text-muted);
  font-size: 0.9rem;
}

.presets .preset-buttons {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.preset {
  background: var(--panel-light);
  border: 1px solid #475569;
  border-radius: 999px;
  padding: 0.45rem 0.9rem;
  color: var(--text);
  font-size: 0.85rem;
  cursor: pointer;
  transition: background 0.15s ease, border-color 0.15s ease;
}

.preset:hover {
  background: #475569;
  border-color: var(--accent);
}

#visualizer {
  width: 100%;
  height: 160px;
  margin-top: 1.5rem;
  background: #020617;
  border-radius: 14px;
  display: block;
}

footer {
  margin-top: 1.25rem;
  text-align: center;
  color: var(--text-muted);
  font-size: 0.85rem;
}

kbd {
  background: var(--panel-light);
  border-radius: 6px;
  padding: 0.15rem 0.4rem;
  font-family: inherit;
  font-size: 0.85em;
}

@media (max-width: 480px) {
  .frequency-readout {
    font-size: 2.5rem;
  }

  .play-button {
    width: 60px;
    height: 60px;
    font-size: 1.5rem;
  }

  main {
    padding: 1.25rem;
  }

  header {
    padding: 1.5rem 1.25rem 1rem;
  }
}