:root {
  --bg: #f2f4f8;
  --primary: #1d4ed8;
  --accent: #f97316;
  --text: #1f2937;
  --grid-border: #111827;
  --hint-bg: #e5e7eb;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: 'Zen Kaku Gothic New', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.hero {
  text-align: center;
  padding: 3rem 1rem 2rem;
  background: linear-gradient(135deg, rgba(29, 78, 216, 0.9), rgba(249, 115, 22, 0.85));
  color: #fff;
  box-shadow: 0 4px 20px rgba(15, 23, 42, 0.2);
}

.hero h1 {
  font-size: clamp(2.2rem, 4vw, 3.1rem);
  margin-bottom: 0.5rem;
}

.hero p {
  font-size: 1.05rem;
  margin: 0;
}

main {
  width: min(960px, 92vw);
  margin: 0 auto;
  flex: 1;
  padding: 2rem 0 4rem;
}

section + section {
  margin-top: 2.5rem;
}

.instructions ol {
  padding-left: 1.2rem;
}

.instructions li {
  margin: 0.4rem 0;
}

.note {
  margin-top: 1rem;
  font-size: 0.95rem;
  color: #4b5563;
}

.board-section {
  display: grid;
  gap: 1.5rem;
  justify-items: center;
}

.board {
  display: grid;
  grid-template-columns: repeat(3, minmax(120px, 1fr));
  gap: 0;
  border: 4px solid var(--grid-border);
  border-radius: 18px;
  overflow: hidden;
  background: #fff;
  box-shadow: 0 12px 25px rgba(15, 23, 42, 0.15);
}

.cell {
  position: relative;
  width: min(30vw, 160px);
  aspect-ratio: 1 / 1;
  border: 2px solid var(--grid-border);
  background: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  touch-action: none;
}

.cell.hint {
  background: var(--hint-bg);
  font-size: clamp(2.8rem, 8vw, 3.4rem);
  font-weight: 700;
  color: var(--grid-border);
}

.cell canvas {
  width: 100%;
  height: 100%;
  background: #fff;
  touch-action: none;
  border-radius: 12px;
}

.cell-controls {
  position: absolute;
  inset: 8px;
  pointer-events: none;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
}

.recognized-value {
  align-self: flex-start;
  background: rgba(255, 255, 255, 0.9);
  padding: 0.2rem 0.5rem;
  border-radius: 999px;
  font-size: clamp(1.6rem, 6vw, 2.2rem);
  font-weight: 600;
  color: var(--primary);
  pointer-events: auto;
}

.manual-input {
  align-self: flex-end;
  display: flex;
  gap: 0.4rem;
  pointer-events: auto;
}

.manual-input input {
  width: 3ch;
  padding: 0.2rem 0.4rem;
  font-size: 1.1rem;
  text-align: center;
  border: 1px solid #cbd5f5;
  border-radius: 6px;
}

.manual-input button {
  border: none;
  background: var(--accent);
  color: #fff;
  padding: 0.3rem 0.6rem;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.9rem;
}

.manual-input button:hover,
.manual-input button:focus {
  background: #fb923c;
}

.board-actions {
  display: flex;
  gap: 1rem;
}

.board-actions button {
  padding: 0.8rem 1.6rem;
  font-size: 1.05rem;
  border: none;
  border-radius: 999px;
  cursor: pointer;
  font-weight: 600;
  background: var(--primary);
  color: #fff;
  box-shadow: 0 8px 18px rgba(29, 78, 216, 0.25);
  transition: transform 0.15s ease, box-shadow 0.15s ease;
}

.board-actions button:hover,
.board-actions button:focus {
  transform: translateY(-2px);
  box-shadow: 0 12px 24px rgba(29, 78, 216, 0.3);
}

.board-actions button:nth-child(2) {
  background: #475569;
  box-shadow: 0 8px 18px rgba(71, 85, 105, 0.25);
}

.board-actions button:nth-child(2):hover,
.board-actions button:nth-child(2):focus {
  box-shadow: 0 12px 24px rgba(71, 85, 105, 0.3);
}

#statusMessage {
  min-height: 1.6rem;
  font-weight: 600;
  color: var(--primary);
}

#statusMessage.error {
  color: #dc2626;
}

.about p {
  line-height: 1.7;
}

footer {
  text-align: center;
  padding: 1.5rem 0 2rem;
  font-size: 0.85rem;
  color: #6b7280;
}

@media (max-width: 640px) {
  .board {
    grid-template-columns: repeat(3, minmax(100px, 1fr));
  }

  .cell {
    width: min(32vw, 140px);
  }
}