:root {
  /* Light Mode - Elegant Warm */
  --bg-primary: #faf8f5;
  --bg-secondary: rgba(255, 255, 255, 0.8);
  --bg-glass: rgba(255, 255, 255, 0.6);
  --board-light: #eecea2;
  --board-dark: #8b5a2b;
  --highlight: rgba(100, 200, 100, 0.7);
  --possible-move: rgba(255, 215, 0, 0.6);
  --selected: rgba(100, 149, 237, 0.7);
  --white-piece: #ffffff;
  --black-piece: #1a1a1a;
  --shadow: rgba(0, 0, 0, 0.15);
  --shadow-strong: rgba(0, 0, 0, 0.25);
  --text-dark: #2c2c2c;
  --text-light: #666666;
  --accent: #b8860b;
  --accent-hover: #daa520;
  --border: rgba(139, 90, 43, 0.3);
  --gradient-1: #d4a574;
  --gradient-2: #8b6914;
}

body.dark-mode {
  /* Dark Mode - Elegant Deep */
  --bg-primary: #0f0f0f;
  --bg-secondary: rgba(30, 30, 30, 0.9);
  --bg-glass: rgba(40, 40, 40, 0.7);
  --board-light: #4a4a4a;
  --board-dark: #2a2a2a;
  --highlight: rgba(100, 200, 100, 0.5);
  --possible-move: rgba(255, 193, 7, 0.5);
  --selected: rgba(70, 130, 180, 0.6);
  --white-piece: #f0f0f0;
  --black-piece: #1a1a1a;
  --shadow: rgba(0, 0, 0, 0.4);
  --shadow-strong: rgba(0, 0, 0, 0.6);
  --text-dark: #e8e8e8;
  --text-light: #aaaaaa;
  --accent: #daa520;
  --accent-hover: #ffd700;
  --border: rgba(218, 165, 32, 0.3);
  --gradient-1: #1a1a1a;
  --gradient-2: #2d2d2d;
}

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

body {
  font-family: 'Inter', 'Segoe UI', sans-serif;
  background: linear-gradient(145deg, var(--gradient-1) 0%, var(--gradient-2) 100%);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  padding: 20px;
  transition: all 0.4s ease;
}

h1, .help-box h3 {
  font-family: 'Playfair Display', Georgia, serif;
}

.game-container {
  flex: 1;
  display: flex;
  flex-direction: column;
  justify-content: center;
  background: var(--bg-primary);
  border-radius: 24px;
  padding: 35px;
  box-shadow: 0 25px 80px var(--shadow-strong),
              0 0 0 1px var(--border);
  max-width: 1200px;
  width: 100%;
  margin: 0 auto;
  backdrop-filter: blur(10px);
  transition: all 0.4s ease;
}

header {
  text-align: center;
  margin-bottom: 30px;
}

.header-top {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 20px;
  margin-bottom: 15px;
  position: relative;
}

h1 {
  color: var(--text-dark);
  font-size: 2.8rem;
  margin: 0;
  font-weight: 400;
  letter-spacing: 0.15em;
  text-transform: uppercase;
  transition: all 0.4s ease;
}

.theme-toggle {
  position: absolute;
  right: 0;
  background: var(--bg-glass);
  border: 1px solid var(--border);
  border-radius: 50%;
  width: 48px;
  height: 48px;
  font-size: 1.4rem;
  cursor: pointer;
  transition: all 0.3s ease;
  box-shadow: 0 4px 15px var(--shadow);
  backdrop-filter: blur(5px);
}

.theme-toggle:hover {
  transform: scale(1.1);
  box-shadow: 0 6px 20px var(--shadow-strong);
  border-color: var(--accent);
}

.info-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 15px;
  flex-wrap: wrap;
  background: var(--bg-glass);
  padding: 16px 28px;
  border-radius: 16px;
  box-shadow: 0 4px 20px var(--shadow);
  border: 1px solid var(--border);
  backdrop-filter: blur(8px);
  transition: all 0.4s ease;
}

.turn-indicator {
  font-size: 1.1rem;
  font-weight: 600;
  color: #1a1a1a;
  padding: 10px 20px;
  background: linear-gradient(135deg, var(--accent) 0%, var(--accent-hover) 100%);
  border-radius: 25px;
  letter-spacing: 0.05em;
  box-shadow: 0 4px 15px rgba(184, 134, 11, 0.3);
  transition: all 0.3s ease;
}

.ai-controls {
  display: flex;
  align-items: center;
  gap: 10px;
}

.ai-controls label {
  color: var(--text-dark);
  font-weight: 500;
  font-size: 0.95rem;
}

.ai-controls select {
  padding: 10px 16px;
  background: var(--bg-primary);
  color: var(--text-dark);
  border: 2px solid var(--border);
  border-radius: 12px;
  font-family: inherit;
  font-size: 0.9rem;
  cursor: pointer;
  transition: all 0.3s ease;
  outline: none;
}

.ai-controls select:hover,
.ai-controls select:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px rgba(184, 134, 11, 0.15);
}

.ai-controls select option {
  background: var(--bg-primary);
  color: var(--text-dark);
  padding: 8px;
}

.btn {
  padding: 12px 28px;
  background: transparent;
  color: var(--text-dark);
  border: 2px solid var(--accent);
  border-radius: 25px;
  font-size: 0.95rem;
  font-weight: 600;
  font-family: inherit;
  letter-spacing: 0.05em;
  cursor: pointer;
  transition: all 0.3s ease;
}

.btn:hover {
  background: var(--accent);
  color: #ffffff;
  transform: translateY(-2px);
  box-shadow: 0 8px 25px rgba(184, 134, 11, 0.4);
}

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

.game-wrapper {
  display: flex;
  justify-content: center;
  align-items: flex-start;
  gap: 20px;
  margin-bottom: 20px;
}

.board-controls {
  display: flex;
  justify-content: center;
  margin: 0 0 20px 0;
}

.btn-restart {
  padding: 14px 32px;
  font-size: 1rem;
}

.chessboard {
  display: grid;
  grid-template-columns: repeat(8, 70px);
  grid-template-rows: repeat(8, 70px);
  gap: 0;
  border: 8px solid var(--board-dark);
  border-radius: 4px;
  overflow: hidden;
  box-shadow: 0 15px 50px var(--shadow-strong),
              inset 0 0 0 2px rgba(255, 255, 255, 0.1);
}

.square {
  width: 70px;
  height: 70px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: all 0.2s ease;
  position: relative;
  font-size: 3.2rem;
  user-select: none;
}

.square.light {
  background-color: var(--board-light);
}

.square.dark {
  background-color: var(--board-dark);
}

.square:hover {
  filter: brightness(1.15);
}

.square.selected {
  background-color: var(--selected) !important;
  box-shadow: inset 0 0 25px rgba(0, 0, 0, 0.4);
}

.square.possible-move {
  background-color: var(--possible-move) !important;
  cursor: pointer;
}

.square.possible-move::after {
  content: '';
  position: absolute;
  width: 24px;
  height: 24px;
  background: rgba(0, 0, 0, 0.25);
  border-radius: 50%;
}

@keyframes pulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.02); }
}

.piece {
  filter: drop-shadow(2px 3px 3px rgba(0, 0, 0, 0.4));
  transition: transform 0.15s ease;
  cursor: grab;
}

.piece:hover {
  transform: scale(1.1);
}

.piece:active {
  cursor: grabbing;
}

.captured {
  background: var(--bg-glass);
  border-radius: 16px;
  padding: 18px;
  min-width: 140px;
  box-shadow: 0 4px 20px var(--shadow);
  border: 1px solid var(--border);
  backdrop-filter: blur(8px);
  transition: all 0.4s ease;
}

.captured h3 {
  font-size: 0.85rem;
  font-weight: 600;
  margin-bottom: 12px;
  color: var(--text-light);
  text-align: center;
  text-transform: uppercase;
  letter-spacing: 0.1em;
}

.captured-pieces {
  display: flex;
  flex-wrap: wrap;
  gap: 5px;
  justify-content: center;
  min-height: 50px;
}

.captured-pieces .piece {
  font-size: 2rem;
  opacity: 0.7;
}

.message-box {
  background: var(--bg-glass);
  padding: 18px;
  border-radius: 16px;
  margin-bottom: 20px;
  text-align: center;
  box-shadow: 0 4px 20px var(--shadow);
  border: 1px solid var(--border);
  backdrop-filter: blur(8px);
  transition: all 0.4s ease;
}

.message-box p {
  font-size: 1.05rem;
  color: var(--text-dark);
  font-weight: 500;
  letter-spacing: 0.02em;
}

.help-box {
  background: var(--bg-glass);
  padding: 24px;
  border-radius: 16px;
  box-shadow: 0 4px 20px var(--shadow);
  border: 1px solid var(--border);
  backdrop-filter: blur(8px);
  transition: all 0.4s ease;
}

.help-box h3 {
  color: var(--text-dark);
  margin-bottom: 18px;
  text-align: center;
  font-weight: 500;
  letter-spacing: 0.05em;
}

.help-box ul {
  list-style: none;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 12px;
}

.help-box li {
  padding: 12px 16px;
  background: var(--bg-primary);
  border-radius: 12px;
  color: var(--text-dark);
  font-size: 0.9rem;
  border: 1px solid var(--border);
  transition: all 0.3s ease;
}

.help-box li:hover {
  border-color: var(--accent);
  transform: translateY(-2px);
}

.help-box strong {
  color: var(--accent);
}

/* Responsive */
@media (max-width: 900px) {
  .game-wrapper {
    flex-direction: column;
    align-items: center;
  }

  .chessboard {
    grid-template-columns: repeat(8, 60px);
    grid-template-rows: repeat(8, 60px);
  }

  .square {
    width: 60px;
    height: 60px;
    font-size: 2.5rem;
  }

  .captured {
    width: 100%;
    max-width: 480px;
  }

  h1 {
    font-size: 2rem;
  }

  .help-box ul {
    grid-template-columns: 1fr;
  }
}