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

  --player-color: #EF4444;
  --player-glow: rgba(239, 68, 68, 0.5);
  --ai-color: #EAB308;
  --ai-glow: rgba(234, 179, 8, 0.5);
  --cell-size: min(62px, calc((100vw - 48px) / 7));
}

@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;
    --border: #D0D7DE;
    --btn-bg: #E9ECF0;
    --btn-active: #D0D7DE;
    --overlay-bg: rgba(255, 255, 255, 0.9);
    --board-bg: #F0F2F5;
    --player-color: #DC2626;
    --player-glow: rgba(220, 38, 38, 0.4);
    --ai-color: #CA8A04;
    --ai-glow: rgba(202, 138, 4, 0.4);
  }
}

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

html, body {
  height: 100%;
  height: 100dvh;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Pretendard', 'Segoe UI', Roboto, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 100dvh;
  overflow: hidden;
  position: relative;
}

/* ── Overlay Screens ── */
.overlay {
  position: fixed;
  inset: 0;
  background: var(--overlay-bg);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  z-index: 100;
  padding: 24px;
  gap: 20px;
  transition: opacity 0.3s ease;
}

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

/* ── Title ── */
.game-title {
  font-size: clamp(40px, 12vw, 60px);
  font-weight: 900;
  letter-spacing: -2px;
  background: linear-gradient(135deg, var(--player-color) 0%, var(--accent) 50%, var(--ai-color) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  text-align: center;
  line-height: 1;
  filter: drop-shadow(0 0 20px rgba(59, 130, 246, 0.3));
}

.game-subtitle {
  font-size: 13px;
  color: var(--text-muted);
  text-align: center;
  letter-spacing: 2px;
  text-transform: uppercase;
  margin-top: -8px;
}

/* ── Stats Bar ── */
.stats-bar {
  display: flex;
  gap: 8px;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 10px 16px;
  width: 100%;
  max-width: 320px;
  justify-content: space-between;
}

.stat-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 2px;
}

.stat-label {
  font-size: 10px;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 1px;
}

.stat-value {
  font-size: 22px;
  font-weight: 800;
  color: var(--text-primary);
}

.stat-item.wins .stat-value { color: var(--player-color); }
.stat-item.losses .stat-value { color: var(--ai-color); }
.stat-item.draws .stat-value { color: var(--text-secondary); }

/* ── Difficulty ── */
.section-label {
  font-size: 11px;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 1.5px;
  align-self: flex-start;
  margin-bottom: -8px;
}

.difficulty-row {
  display: flex;
  gap: 8px;
  width: 100%;
  max-width: 320px;
}

.diff-btn {
  flex: 1;
  padding: 10px 4px;
  background: var(--btn-bg);
  border: 1.5px solid var(--border);
  border-radius: 10px;
  color: var(--text-secondary);
  font-size: 12px;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.15s ease;
  font-family: inherit;
  letter-spacing: 0.3px;
}

.diff-btn:hover {
  background: var(--btn-active);
  color: var(--text-primary);
  border-color: var(--accent);
}

.diff-btn.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
  box-shadow: 0 0 12px rgba(59, 130, 246, 0.4);
}

/* ── Buttons ── */
.btn-primary {
  width: 100%;
  max-width: 320px;
  padding: 14px;
  background: var(--accent);
  border: none;
  border-radius: 12px;
  color: #fff;
  font-size: 16px;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.15s ease;
  font-family: inherit;
  letter-spacing: 0.3px;
  box-shadow: 0 4px 16px rgba(59, 130, 246, 0.35);
}

.btn-primary:hover {
  transform: translateY(-1px);
  box-shadow: 0 6px 20px rgba(59, 130, 246, 0.45);
}

.btn-primary:active {
  transform: translateY(0);
}

.btn-secondary {
  width: 100%;
  max-width: 320px;
  padding: 12px;
  background: var(--btn-bg);
  border: 1.5px solid var(--border);
  border-radius: 12px;
  color: var(--text-secondary);
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.15s ease;
  font-family: inherit;
}

.btn-secondary:hover {
  background: var(--btn-active);
  color: var(--text-primary);
  border-color: var(--text-muted);
}

/* ── Result Overlay ── */
.result-icon {
  font-size: 64px;
  line-height: 1;
  filter: drop-shadow(0 0 16px rgba(255,255,255,0.2));
}

.result-title {
  font-size: clamp(28px, 8vw, 40px);
  font-weight: 900;
  text-align: center;
  letter-spacing: -1px;
}

.result-title.win {
  color: var(--player-color);
  text-shadow: 0 0 20px var(--player-glow);
}

.result-title.loss {
  color: var(--ai-color);
  text-shadow: 0 0 20px var(--ai-glow);
}

.result-title.draw {
  color: var(--text-secondary);
}

.result-subtitle {
  font-size: 14px;
  color: var(--text-muted);
  text-align: center;
}

/* ── Main Game Layout ── */
#game-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  width: 100%;
  max-width: 480px;
  padding: 16px;
  gap: 14px;
}

/* ── Header ── */
.game-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
}

.header-title {
  font-size: 20px;
  font-weight: 800;
  letter-spacing: -0.5px;
  background: linear-gradient(135deg, var(--player-color), var(--accent));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.header-controls {
  display: flex;
  gap: 8px;
}

.icon-btn {
  width: 36px;
  height: 36px;
  background: var(--btn-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text-secondary);
  font-size: 15px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.15s ease;
  font-family: inherit;
}

.icon-btn:hover {
  background: var(--btn-active);
  color: var(--text-primary);
  border-color: var(--text-muted);
}

/* ── Turn Indicator ── */
.turn-indicator {
  display: flex;
  align-items: center;
  gap: 10px;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 10px 16px;
  width: 100%;
  transition: all 0.3s ease;
}

.turn-disc {
  width: 20px;
  height: 20px;
  border-radius: 50%;
  flex-shrink: 0;
  transition: background 0.3s ease, box-shadow 0.3s ease;
}

.turn-disc.player {
  background: var(--player-color);
  box-shadow: 0 0 8px var(--player-glow);
}

.turn-disc.ai {
  background: var(--ai-color);
  box-shadow: 0 0 8px var(--ai-glow);
}

.turn-text {
  font-size: 14px;
  font-weight: 600;
  color: var(--text-primary);
  flex: 1;
}

.turn-hint {
  font-size: 12px;
  color: var(--text-muted);
}

/* ── Board ── */
.board-wrapper {
  position: relative;
  width: 100%;
}

#board {
  display: grid;
  grid-template-columns: repeat(7, var(--cell-size));
  grid-template-rows: repeat(6, var(--cell-size));
  gap: 5px;
  background: var(--board-bg);
  border: 1.5px solid var(--border);
  border-radius: 16px;
  padding: 10px;
  margin: 0 auto;
  width: fit-content;
}

/* ── Column Hover Zones ── */
.col-hover-zone {
  position: absolute;
  top: 0;
  bottom: 0;
  cursor: pointer;
  transition: background 0.15s ease;
  border-radius: 16px;
}

.col-hover-zone:hover {
  background: rgba(59, 130, 246, 0.06);
}

/* ── Cell ── */
.cell {
  width: var(--cell-size);
  height: var(--cell-size);
  border-radius: 50%;
  background: var(--bg-secondary);
  border: 1.5px solid var(--border);
  position: relative;
  overflow: hidden;
  transition: border-color 0.15s ease;
}

.cell::after {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: 50%;
  opacity: 0;
  transition: opacity 0.3s ease;
}

/* ── Preview dot ── */
.cell.preview-player::after {
  background: var(--player-color);
  opacity: 0.25;
}

.cell.preview-ai::after {
  background: var(--ai-color);
  opacity: 0.25;
}

/* ── Disc ── */
.disc {
  position: absolute;
  inset: 0;
  border-radius: 50%;
  opacity: 0;
}

.disc.player {
  background: radial-gradient(circle at 35% 35%, #F87171, var(--player-color) 70%);
  box-shadow: inset 0 -3px 6px rgba(0,0,0,0.3), 0 0 8px var(--player-glow);
}

.disc.ai {
  background: radial-gradient(circle at 35% 35%, #FDE68A, var(--ai-color) 70%);
  box-shadow: inset 0 -3px 6px rgba(0,0,0,0.3), 0 0 8px var(--ai-glow);
}

/* ── Drop Animation ── */
@keyframes dropIn {
  0% { transform: translateY(calc(-1 * var(--drop-distance))); opacity: 1; }
  80% { transform: translateY(6px); opacity: 1; }
  90% { transform: translateY(-3px); opacity: 1; }
  100% { transform: translateY(0); opacity: 1; }
}

.disc.dropping {
  opacity: 1;
  animation: dropIn 0.38s cubic-bezier(0.4, 0, 0.2, 1) forwards;
}

.disc.placed {
  opacity: 1;
}

/* ── Win Highlight ── */
@keyframes winPulse {
  0%, 100% { transform: scale(1); box-shadow: inset 0 -3px 6px rgba(0,0,0,0.3), 0 0 10px currentColor; }
  50% { transform: scale(1.08); box-shadow: inset 0 -3px 6px rgba(0,0,0,0.2), 0 0 22px currentColor; }
}

.cell.winning .disc {
  animation: winPulse 0.9s ease-in-out infinite;
}

.cell.winning.player-win .disc {
  color: var(--player-glow);
}

.cell.winning.ai-win .disc {
  color: var(--ai-glow);
}

/* ── AI Thinking ── */
.thinking-dots {
  display: inline-flex;
  gap: 3px;
}

.thinking-dots span {
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: var(--ai-color);
  animation: blink 1.2s ease-in-out infinite;
}

.thinking-dots span:nth-child(2) { animation-delay: 0.2s; }
.thinking-dots span:nth-child(3) { animation-delay: 0.4s; }

@keyframes blink {
  0%, 80%, 100% { opacity: 0.2; transform: scale(0.85); }
  40% { opacity: 1; transform: scale(1); }
}

/* ── Mini Stats in header area ── */
.mini-stats {
  display: flex;
  gap: 12px;
}

.mini-stat {
  font-size: 12px;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 4px;
}

.mini-stat .dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
}

.mini-stat .dot.red { background: var(--player-color); }
.mini-stat .dot.yellow { background: var(--ai-color); }

/* ── Responsive ── */
@media (max-height: 700px) {
  #game-container {
    gap: 10px;
    padding: 10px;
  }

  .turn-indicator {
    padding: 8px 12px;
  }

  .game-header {
    padding-bottom: 2px;
  }
}

@media (max-width: 380px) {
  :root {
    --cell-size: min(52px, calc((100vw - 36px) / 7));
  }

  #board {
    gap: 4px;
    padding: 7px;
  }
}