:root {
  --bg-primary: #0D1117;
  --bg-secondary: #161B22;
  --bg-tertiary: #21262D;
  --text-primary: #F0F6FC;
  --text-secondary: #8B949E;
  --text-muted: #484F58;
  --accent: #3B82F6;
  --accent-glow: rgba(59, 130, 246, 0.3);
  --border: #30363D;
  --btn-bg: #21262D;
  --btn-active: #30363D;
  --overlay-bg: rgba(0, 0, 0, 0.85);
  --board-bg: #0A0E14;
}

@media (prefers-color-scheme: light) {
  :root {
    --bg-primary: #FFFFFF;
    --bg-secondary: #F6F8FA;
    --bg-tertiary: #E9ECF0;
    --text-primary: #1B1E28;
    --text-secondary: #57606A;
    --text-muted: #8C959F;
    --accent: #3182F6;
    --accent-glow: rgba(49, 130, 246, 0.2);
    --border: #D0D7DE;
    --btn-bg: #E9ECF0;
    --btn-active: #D0D7DE;
    --overlay-bg: rgba(255, 255, 255, 0.9);
    --board-bg: #F0F2F5;
  }
}

.hidden { display: none !important; }

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

html, body {
  height: 100%;
  width: 100%;
  overflow: hidden;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Pretendard', 'Segoe UI', Roboto, sans-serif;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100dvh;
  height: 100dvh;
  touch-action: manipulation;
  -webkit-tap-highlight-color: transparent;
  user-select: none;
  -webkit-user-select: none;
}

#app {
  position: relative;
  width: 100%;
  max-width: 480px;
  height: 100dvh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  overflow: hidden;
}

/* ─── Overlay Screens ─── */
.overlay {
  position: absolute;
  inset: 0;
  z-index: 100;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 20px;
  padding: 32px 24px;
  background: var(--overlay-bg);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  transition: opacity 0.3s ease, visibility 0.3s ease;
}

.overlay.hidden {
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
}

/* ─── Title / Brand ─── */
.game-title {
  font-size: clamp(2.8rem, 12vw, 4.2rem);
  font-weight: 800;
  letter-spacing: 0.12em;
  background: linear-gradient(135deg, #3B82F6, #8B5CF6, #EC4899);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  text-shadow: none;
  line-height: 1;
}

.game-subtitle {
  font-size: 1rem;
  color: var(--text-secondary);
  text-align: center;
  line-height: 1.6;
  max-width: 280px;
}

/* ─── Stats Row (start screen) ─── */
.stats-row {
  display: flex;
  gap: 16px;
  margin: 4px 0;
}

.stat-box {
  flex: 1;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 14px 12px;
  text-align: center;
}

.stat-box .stat-value {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--accent);
}

.stat-box .stat-label {
  font-size: 0.7rem;
  color: var(--text-muted);
  margin-top: 2px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* ─── Buttons ─── */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 14px 28px;
  border-radius: 12px;
  border: 1px solid var(--border);
  background: var(--btn-bg);
  color: var(--text-primary);
  font-family: inherit;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  min-width: 160px;
  transition: background 0.15s, transform 0.1s, box-shadow 0.15s;
  -webkit-tap-highlight-color: transparent;
}

.btn:active {
  background: var(--btn-active);
  transform: scale(0.97);
}

.btn-primary {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
  box-shadow: 0 0 16px var(--accent-glow);
}

.btn-primary:active {
  background: var(--accent);
  box-shadow: 0 0 8px var(--accent-glow);
}

.btn-row {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
  justify-content: center;
}

/* ─── Victory panel ─── */
.result-panel {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 20px 24px;
  width: 100%;
  max-width: 320px;
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.result-title {
  font-size: 1.5rem;
  font-weight: 700;
  text-align: center;
  background: linear-gradient(135deg, #3B82F6, #8B5CF6, #EC4899);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

.result-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.9rem;
}

.result-row .label {
  color: var(--text-secondary);
}

.result-row .value {
  font-weight: 700;
  color: var(--text-primary);
}

.result-row .value.record {
  color: #F59E0B;
}

.record-badge {
  display: inline-block;
  background: #F59E0B22;
  color: #F59E0B;
  border: 1px solid #F59E0B55;
  border-radius: 6px;
  padding: 2px 8px;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  margin-left: 6px;
}

/* ─── Game Screen ─── */
#game-screen {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 24px;
  width: 100%;
  padding: 24px 16px;
}

.hud {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  max-width: 340px;
}

.hud-item {
  text-align: center;
}

.hud-item .hud-value {
  font-size: 1.6rem;
  font-weight: 700;
  color: var(--text-primary);
  line-height: 1;
}

.hud-item .hud-label {
  font-size: 0.68rem;
  color: var(--text-muted);
  margin-top: 3px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
}

.hud-sep {
  width: 1px;
  height: 36px;
  background: var(--border);
}

/* ─── Board ─── */
.board-wrapper {
  background: var(--board-bg);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 12px;
}

#board {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 8px;
}

.cell {
  width: clamp(48px, 13vw, 62px);
  height: clamp(48px, 13vw, 62px);
  border-radius: 10px;
  background: var(--bg-tertiary);
  border: 1.5px solid var(--border);
  cursor: pointer;
  transition: background-color 0.18s ease, box-shadow 0.18s ease, transform 0.08s ease, border-color 0.18s ease;
  position: relative;
  overflow: hidden;
}

.cell::after {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: radial-gradient(circle at 40% 35%, rgba(255,255,255,0.18), transparent 65%);
  opacity: 0;
  transition: opacity 0.18s ease;
  pointer-events: none;
}

.cell.on {
  background-color: var(--accent);
  border-color: var(--accent);
  box-shadow:
    0 0 10px var(--accent-glow),
    0 0 22px var(--accent-glow),
    inset 0 1px 0 rgba(255,255,255,0.2);
}

.cell.on::after {
  opacity: 1;
}

.cell:active {
  transform: scale(0.93);
}

.cell.hint {
  border-color: #F59E0B;
  box-shadow: 0 0 12px rgba(245, 158, 11, 0.5), 0 0 24px rgba(245, 158, 11, 0.25);
  animation: hint-pulse 1s ease-in-out infinite;
}

.cell.hint.on {
  box-shadow:
    0 0 10px var(--accent-glow),
    0 0 22px var(--accent-glow),
    0 0 12px rgba(245, 158, 11, 0.5),
    inset 0 1px 0 rgba(255,255,255,0.2);
}

@keyframes hint-pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.65; }
}

/* ─── Action bar ─── */
.action-bar {
  display: flex;
  gap: 10px;
  align-items: center;
}

.btn-sm {
  padding: 10px 18px;
  font-size: 0.85rem;
  min-width: 0;
  border-radius: 10px;
}

.btn-hint {
  background: var(--btn-bg);
  border-color: var(--border);
  color: var(--text-secondary);
  position: relative;
}

.hint-count {
  position: absolute;
  top: -6px;
  right: -6px;
  background: #F59E0B;
  color: #000;
  font-size: 0.65rem;
  font-weight: 800;
  border-radius: 50%;
  width: 18px;
  height: 18px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.btn-hint.no-hints {
  opacity: 0.45;
  cursor: not-allowed;
}

/* ─── Level badge ─── */
.level-badge {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 4px 12px;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 20px;
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text-secondary);
}

.level-badge .lv-num {
  color: var(--accent);
  font-weight: 800;
}

/* ─── Responsive tweaks ─── */
@media (max-height: 640px) {
  #game-screen { gap: 14px; }
  .board-wrapper { padding: 8px; }
  #board { gap: 6px; }
  .cell {
    width: clamp(40px, 11vw, 54px);
    height: clamp(40px, 11vw, 54px);
  }
  .hud { gap: 4px; }
}