:root {
  /* Default classic wood theme */
  --board-light: #f0d9b5;
  --board-dark: #b58863;
  --bg-color: #f8fafc;
  --panel-bg: rgba(255, 255, 255, 0.9);
  --panel-border: rgba(0, 0, 0, 0.08);
  --text-main: #1e293b;
  --text-muted: #64748b;
  --accent: #334155;
  --btn-bg: #e2e8f0;
  --btn-hover: #cbd5e1;
  --btn-text: #0f172a;
  
  --highlighted: rgba(234, 230, 48, 0.5); /* Last move */
  --selected: rgba(20, 130, 40, 0.45);    /* Selected piece */
  --hint-empty: rgba(0, 0, 0, 0.15);      /* Legal move dot */
  --hint-capture: rgba(0, 0, 0, 0.2);     /* Capture ring */
  --danger: rgba(220, 53, 69, 0.85);      /* King in check */
  
  --border-radius: 12px;
  --shadow-sm: 0 4px 6px -1px rgb(0 0 0 / 0.1);
  --shadow-md: 0 10px 25px -3px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 25px 50px -12px rgb(0 0 0 / 0.25);
  --font-heading: 'Crimson Text', Georgia, serif;
  --font-ui: 'Inter', system-ui, -apple-system, sans-serif;
  --blur: blur(12px);
}

[data-theme="slate"] {
  --board-light: #e2e8f0;
  --board-dark: #64748b;
  --bg-color: #0f172a;
  --panel-bg: rgba(30, 41, 59, 0.85);
  --panel-border: rgba(255, 255, 255, 0.1);
  --text-main: #f8fafc;
  --text-muted: #94a3b8;
  --accent: #3b82f6;
  --btn-bg: #334155;
  --btn-hover: #475569;
  --btn-text: #f8fafc;
}

[data-theme="ocean"] {
  --board-light: #dbeafe;
  --board-dark: #3b82f6;
  --bg-color: #172554;
  --panel-bg: rgba(30, 58, 138, 0.85);
  --panel-border: rgba(255, 255, 255, 0.1);
  --text-main: #eff6ff;
  --text-muted: #93c5fd;
  --accent: #f59e0b;
  --btn-bg: #1e3a8a;
  --btn-hover: #2563eb;
  --btn-text: #eff6ff;
}

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

body {
  font-family: var(--font-ui);
  background: var(--bg-color);
  color: var(--text-main);
  line-height: 1.6;
  min-height: 100vh;
  transition: background 0.4s ease, color 0.4s ease;
  overflow-x: hidden;
  overscroll-behavior-y: none; /* Block native pull-to-refresh on mobile */
  -webkit-tap-highlight-color: transparent; /* Remove active link blue flashing */
  touch-action: manipulation; /* Block arbitrary double-tap zooming */
  user-select: none;
}

input, select, button { cursor: pointer; } 

h1, h2, h3, .subtitle, .turn-indicator {
  font-family: var(--font-heading);
}

.app-container {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  padding: max(1.5rem, env(safe-area-inset-top)) max(1.5rem, env(safe-area-inset-right)) max(1.5rem, env(safe-area-inset-bottom)) max(1.5rem, env(safe-area-inset-left));
}

.app-header {
  text-align: center;
  margin-bottom: 2rem;
  z-index: 10; /* Z-INDEX: Above background, below modals */
}

.app-header h1 {
  font-size: 2.8rem;
  font-weight: 600;
  letter-spacing: 1px;
  color: var(--text-main);
  text-shadow: 0 2px 4px rgba(0,0,0,0.05);
}

.subtitle {
  font-size: 1.2rem;
  color: var(--text-muted);
  font-style: italic;
  font-family: var(--font-ui);
}

/* LAYOUT */
.game-layout {
  display: flex;
  gap: 3rem;
  justify-content: center;
  align-items: flex-start;
  flex-grow: 1;
  max-width: 1300px;
  margin: 0 auto;
  width: 100%;
}

.board-section {
  flex: 0 0 auto;
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
  width: 100%;
  max-width: 640px;
}

.sidebar {
  flex: 1 1 320px;
  max-width: 380px;
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
  animation: slideFade 0.5s ease;
}

@keyframes slideFade {
  from { opacity: 0; transform: translateX(20px); }
  to { opacity: 1; transform: translateX(0); }
}

/* STATUS BAR */
.status-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: var(--panel-bg);
  padding: 1rem 1.5rem;
  border-radius: var(--border-radius);
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--panel-border);
  backdrop-filter: var(--blur);
  -webkit-backdrop-filter: var(--blur);
  transition: all 0.3s ease;
}

.turn-indicator {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-size: 1.3rem;
  font-weight: 600;
}

.indicator-dot {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: currentColor;
  box-shadow: 0 0 10px currentColor;
  animation: pulse 2s infinite;
}

@keyframes pulse {
  0% { transform: scale(0.95); box-shadow: 0 0 0 0 rgba(0,0,0,0.3); }
  70% { transform: scale(1.05); box-shadow: 0 0 0 6px rgba(0,0,0,0); }
  100% { transform: scale(0.95); box-shadow: 0 0 0 0 rgba(0,0,0,0); }
}

.score-display {
  font-family: var(--font-ui);
  font-weight: 500;
  font-size: 1.1rem;
  color: var(--text-muted);
  background: rgba(0,0,0,0.05);
  padding: 0.25rem 0.75rem;
  border-radius: 20px;
}

/* CHESS BOARD */
.board-wrapper {
  position: relative;
  background: var(--panel-bg);
  padding: 1.25rem;
  border-radius: calc(var(--border-radius) + 8px);
  box-shadow: var(--shadow-md);
  border: 1px solid var(--panel-border);
  backdrop-filter: var(--blur);
  -webkit-backdrop-filter: var(--blur);
}

.board-layout {
  display: grid;
  grid-template-columns: 20px 1fr;
  grid-template-rows: 1fr 20px;
  gap: 8px;
  align-items: center;
}

.coords-rank {
  display: flex;
  flex-direction: column;
  height: 100%;
  justify-content: space-around;
  align-items: center;
  font-family: var(--font-ui);
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--text-muted);
  user-select: none;
}

.coords-file {
  display: flex;
  width: 100%;
  justify-content: space-around;
  align-items: center;
  font-family: var(--font-ui);
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--text-muted);
  user-select: none;
}

.chess-board {
  display: grid;
  grid-template-columns: repeat(8, 1fr);
  grid-template-rows: repeat(8, 1fr);
  width: 100%;
  aspect-ratio: 1;
  border: 4px solid var(--text-main);
  border-radius: 6px;
  overflow: hidden;
  box-shadow: inset 0 0 10px rgba(0,0,0,0.1);
  margin: 0 auto;
  touch-action: none;
}

.square {
  position: relative;
  display: flex;
  justify-content: center;
  align-items: center;
  user-select: none;
  transition: background-color 0.15s ease;
}

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

.square.selected::after {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  box-shadow: inset 0 0 0 4px rgba(255,255,255,0.7);
  background-color: var(--selected);
  pointer-events: none;
}
.square.highlight::after {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  background-color: var(--highlighted);
  pointer-events: none;
}
.square.in-check::after {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  background: radial-gradient(circle, transparent 20%, var(--danger) 100%);
  pointer-events: none;
}

#arrows-layer {
  position: absolute;
  top: 0; left: 0; width: 100%; height: 100%;
  pointer-events: none;
  z-index: 25;
}

.square:hover::after {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  background: rgba(255, 255, 255, 0.15);
  pointer-events: none;
}

/* Pieces */
.piece {
  font-size: calc(3vw + 1.2rem);
  line-height: 1;
  cursor: pointer;
  z-index: 10;
  transition: transform 0.15s ease-out, filter 0.15s ease-out;
  will-change: transform;
}
@media (min-width: 800px) {
  .piece { font-size: 3.8rem; }
}

.piece:hover {
  transform: scale(1.12);
  filter: drop-shadow(0 6px 8px rgba(0,0,0,0.4));
}

.white-piece {
  color: #ffffff;
  -webkit-text-stroke: 1.5px #1a1a1a;
  filter: drop-shadow(0 3px 3px rgba(0,0,0,0.4));
}
.black-piece {
  color: #1a1a1a;
  -webkit-text-stroke: 1.5px #0a0a0a;
  filter: drop-shadow(0 2px 2px rgba(255,255,255,0.15)) drop-shadow(0 4px 4px rgba(0,0,0,0.5));
}

/* Hint Indicators */
.legal-move-dot {
  width: 25%;
  height: 25%;
  background-color: var(--hint-empty);
  border-radius: 50%;
  position: absolute;
  pointer-events: none;
  z-index: 5; /* Z-INDEX: Hint modifiers sit below pieces (10) */
}

.legal-move-capture {
  width: 85%;
  height: 85%;
  border: 5px solid var(--hint-capture);
  border-radius: 50%;
  position: absolute;
  pointer-events: none;
  z-index: 5; /* Z-INDEX: Hint modifiers sit below pieces (10) */
}

/* PANELS */
.panel {
  background: var(--panel-bg);
  border-radius: var(--border-radius);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--panel-border);
  backdrop-filter: var(--blur);
  -webkit-backdrop-filter: var(--blur);
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.panel:hover {
  box-shadow: var(--shadow-md);
}

.panel h3 {
  font-size: 1.15rem;
  margin-bottom: 1rem;
  border-bottom: 2px solid var(--panel-border);
  padding-bottom: 0.5rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  color: var(--text-muted);
}

.btn-group {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
  margin-top: 1rem;
}

.btn-group .btn {
  flex: 1;
}

button.btn {
  background: var(--btn-bg);
  color: var(--btn-text);
  border: 1px solid rgba(0,0,0,0.05);
  padding: 0.8rem 1.2rem;
  font-family: var(--font-ui);
  font-size: 1rem;
  font-weight: 500;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s cubic-bezier(0.175, 0.885, 0.32, 1.275);
  width: 100%;
}

button.btn-animate:hover {
  background: var(--btn-hover);
  transform: translateY(-2px);
  box-shadow: 0 4px 10px rgba(0,0,0,0.1);
}

button.btn-animate:active {
  transform: translateY(1px);
  box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

button.btn.primary {
  background: var(--accent);
  color: #fff;
  border: none;
}
button.btn.primary:hover {
  filter: brightness(1.1);
}

/* Captured/Advantage Info */
.captured-group {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin-bottom: 0.5rem;
}

.captured-row {
  min-height: 2.5rem;
  display: flex;
  flex-wrap: wrap;
  gap: -0.25rem;
  font-size: 1.8rem;
  color: var(--text-main);
  filter: drop-shadow(0 1px 2px rgba(0,0,0,0.2));
}

.adv-badge {
  background: var(--btn-bg);
  padding: 0.2rem 0.6rem;
  border-radius: 12px;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-muted);
}
.adv-badge.hidden { display: none; }

/* History */
.history-list-wrapper {
  max-height: 220px;
  overflow-y: auto;
  padding-right: 0.5rem;
  scroll-behavior: smooth;
}

.history-list-wrapper::-webkit-scrollbar { width: 6px; }
.history-list-wrapper::-webkit-scrollbar-thumb { background: var(--panel-border); border-radius: 10px; }

.history-list {
  list-style: none;
  display: grid;
  grid-template-columns: 2.5rem 1fr 1fr;
  row-gap: 0.35rem;
  column-gap: 0.75rem;
  font-family: monospace;
}

.history-list li.turn-num {
  color: var(--text-muted);
  text-align: right;
  padding-top: 0.3rem;
  font-size: 0.95rem;
}
.move-cell {
  background: rgba(0,0,0,0.03);
  padding: 0.3rem 0.6rem;
  border-radius: 4px;
  font-size: 0.95rem;
  transition: background 0.2s, transform 0.1s;
  cursor: pointer;
  position: relative;
}
[data-theme="slate"] .move-cell, [data-theme="ocean"] .move-cell { background: rgba(255,255,255,0.05); }

.move-cell:empty { cursor: default; background: transparent; }

.move-cell.eval-best { border-left: 3px solid #10b981; }
.move-cell.eval-good { border-left: 3px solid #3b82f6; }
.move-cell.eval-inacc { border-left: 3px solid #f59e0b; }
.move-cell.eval-mistake { border-left: 3px solid #f97316; }
.move-cell.eval-blunder { border-left: 3px solid #ef4444; color: var(--danger) !important; font-weight: 600; }

.eval-text-best { color: #10b981; }
.eval-text-good { color: #3b82f6; }
.eval-text-inacc { color: #f59e0b; }
.eval-text-mistake { color: #f97316; }
.eval-text-blunder { color: #ef4444; text-transform: uppercase; font-weight: 700; }

.move-cell:not(:empty):hover {
  background: var(--highlighted);
}

.move-cell.latest {
  background: var(--selected);
  color: #fff;
  font-weight: 600;
}

/* MODALS */
.modal-overlay {
  position: fixed;
  top: 0; left: 0; width: 100%; height: 100%;
  background: rgba(0,0,0,0.6);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  display: flex;
  justify-content: center;
  align-items: center;
  z-index: 1000; /* Z-INDEX: Full-screen modal overlays, highest layer */
  opacity: 1;
  visibility: visible;
  transition: opacity 0.3s ease, visibility 0.3s ease;
}

.modal-overlay.hidden {
  opacity: 0;
  pointer-events: none; /* Safely removes click interception */
  visibility: hidden; /* Strictly hides element when fully transparent */
}

.modal {
  background: var(--panel-bg);
  color: var(--text-main);
  padding: 2.5rem;
  border-radius: var(--border-radius);
  box-shadow: var(--shadow-lg);
  width: 90%;
  max-width: 440px;
  border: 1px solid var(--panel-border);
}

.fade-in-scale {
  transform: scale(1);
  transition: transform 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

@keyframes winGlow {
  0% { box-shadow: 0 0 10px rgba(16, 185, 129, 0.2), var(--shadow-lg); }
  50% { box-shadow: 0 0 30px rgba(16, 185, 129, 0.6), var(--shadow-lg); }
  100% { box-shadow: 0 0 10px rgba(16, 185, 129, 0.2), var(--shadow-lg); }
}

@keyframes lossShake {
  0% { transform: scale(1) translateX(0); }
  10%, 30%, 50%, 70%, 90% { transform: scale(1) translateX(-3px); }
  20%, 40%, 60%, 80% { transform: scale(1) translateX(3px); }
  100% { transform: scale(1) translateX(0); }
}

.modal.game-over.win-anim {
  animation: winGlow 2s infinite ease-in-out;
  border-color: rgba(16, 185, 129, 0.5);
}

.modal.game-over.loss-anim {
  animation: lossShake 0.6s cubic-bezier(.36,.07,.19,.97) both;
  border-color: rgba(220, 53, 69, 0.5);
}

.modal-overlay.hidden .fade-in-scale {
  transform: scale(0.9);
}

.modal-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1.5rem;
  border-bottom: 1px solid var(--panel-border);
  padding-bottom: 1rem;
}

.modal-header h2 { font-size: 1.5rem; }

.close-modal {
  background: none; border: none; font-size: 1.8rem;
  color: var(--text-muted); cursor: pointer;
  transition: color 0.2s, transform 0.2s;
}
.close-modal:hover { color: var(--danger); transform: rotate(90deg); }

.setting-group {
  margin-bottom: 1.5rem;
}
.setting-title {
  display: block;
  font-weight: 600;
  margin-bottom: 0.75rem;
  color: var(--text-muted);
}
.setting-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.5rem 0;
  cursor: pointer;
}

/* Radio buttons & Inputs */
.radio-group {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}
.radio-btn {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  cursor: pointer;
  background: var(--btn-bg);
  padding: 0.75rem 1rem;
  border-radius: 8px;
  transition: background 0.2s ease;
  border: 1px solid transparent;
}
.radio-btn:hover { background: var(--btn-hover); }
.radio-btn input[type="radio"] { accent-color: var(--accent); transform: scale(1.2); }

.form-input {
  width: 100%;
  padding: 0.75rem;
  border-radius: 8px;
  border: 1px solid var(--panel-border);
  background: var(--bg-color);
  color: var(--text-main);
  font-family: var(--font-ui);
  font-size: 1rem;
}
.form-input:focus { outline: 2px solid var(--accent); }

/* Modifiers */
.full-width { width: 100%; margin-top: 2rem;}
.center-align { text-align: center; justify-content: center; }
.mt-2 { margin-top: 1.5rem; }

/* AI Thinking Overlay */
.ai-thinking-overlay {
  position: absolute;
  top: 50%; left: 50%;
  transform: translate(-50%, -50%);
  background: var(--panel-bg);
  padding: 1.5rem 2rem;
  border-radius: 30px;
  box-shadow: var(--shadow-lg);
  display: flex;
  align-items: center;
  gap: 1rem;
  font-weight: 600;
  z-index: 50; /* Z-INDEX: Local board overlays, above pieces (10) but below full screen modals */
  border: 2px solid var(--accent);
  backdrop-filter: blur(10px);
}
.ai-thinking-overlay.hidden { display: none; }

.spinner {
  width: 24px;
  height: 24px;
  border: 3px solid var(--text-muted);
  border-top-color: var(--accent);
  border-radius: 50%;
  animation: spin 1s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

/* Promotion */
.promotion-modal {
  position: absolute;
  top: 50%; left: 50%;
  transform: translate(-50%, -50%);
  background: var(--panel-bg);
  padding: 2rem;
  border-radius: var(--border-radius);
  box-shadow: var(--shadow-lg);
  text-align: center;
  z-index: 50; /* Z-INDEX: Local board overlays, above pieces (10) but below full screen modals */
  border: 2px solid var(--accent);
}
.promotion-modal.hidden { display: none; }
.promotion-options { display: flex; gap: 1rem; margin-top: 1rem; }
.promo-piece {
  font-size: 3.5rem;
  cursor: pointer;
  padding: 0.5rem;
  border-radius: 12px;
  background: var(--btn-bg);
  transition: transform 0.2s, background 0.2s;
}
.promo-piece:hover { transform: scale(1.1); background: var(--btn-hover); }

/* Responsive tweaks */
@media (max-width: 950px) {
  .game-layout { flex-direction: column; align-items: center; gap: 1.5rem;}
  .board-section, .sidebar { width: 100%; max-width: 600px; }
  .chess-board { aspect-ratio: 1; }
  .piece { font-size: calc(8vw - 1rem); }
}

@media (max-width: 480px) {
  .app-container { 
    padding: max(0.5rem, env(safe-area-inset-top)) max(0.5rem, env(safe-area-inset-right)) max(0.5rem, env(safe-area-inset-bottom)) max(0.5rem, env(safe-area-inset-left));
  }
  .app-header { margin-bottom: 1rem; }
  .app-header h1 { font-size: 1.8rem; letter-spacing: 0.2rem; }
  .panel { padding: 1rem; }
  .piece { font-size: calc(11.5vw - 0.5rem); }
  .modal { padding: 1.25rem; width: 95%; max-height: 90vh; overflow-y: auto;}
  
  /* Make sure history/panels aren't excessively tall on tiny screens */
  .history-list-wrapper { max-height: 180px; }
  .board-section { gap: 0.75rem; }
  .radio-group[style*="grid"] { grid-template-columns: 1fr !important; }
}
@keyframes winJump {
  0%, 100% { transform: translateY(0) scale(1); }
  30% { transform: translateY(-30px) scale(1.1); }
  50% { transform: translateY(0) scale(1); }
  70% { transform: translateY(-15px) scale(1.05); }
}

@keyframes loseBreak {
  0% { transform: rotate(0deg); }
  20% { transform: rotate(-15deg); }
  40% { transform: rotate(90deg) translate(10px, 10px); opacity: 0.6; }
  100% { transform: rotate(90deg) translate(10px, 10px); opacity: 0.6; }
}

@keyframes drawSpin {
  0% { transform: rotate(0deg) scale(1); }
  50% { transform: rotate(180deg) scale(0.8); opacity: 0.7; }
  100% { transform: rotate(360deg) scale(1); }
}

.piece.anim-win-jump {
  animation: winJump 1.5s ease-in-out infinite;
  z-index: 20;
}
.piece.anim-lose-break {
  animation: loseBreak 2s forwards;
  transform-origin: bottom center;
}
.piece.anim-draw {
  animation: drawSpin 3s linear infinite;
}