:root {
  --wood-dark: #5c3d2e;
  --wood-mid: #8b6914;
  --wood-light: #c4a35a;
  --wood-highlight: #e8d4a8;
  --grid-line: rgba(60, 40, 25, 0.55);
  --text: #e8eef8;
  --text-muted: rgba(200, 214, 235, 0.75);
  --bg-page: #060a12;
  --panel: rgba(18, 26, 48, 0.88);
  --panel-border: rgba(120, 160, 255, 0.18);
  --panel-heading: #c7d6f5;
  --black-stone: #1a1a1a;
  --white-stone: #f8f6f2;
  --accent: #38bdf8;
  --accent-dim: #0ea5e9;
  --danger: #f87171;
  --radius: 10px;
  --cell-count: 15;
}

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

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Segoe UI", "PingFang TC", "Microsoft JhengHei", sans-serif;
  color: var(--text);
  background-color: var(--bg-page);
  background-image:
    radial-gradient(ellipse 90% 55% at 50% -15%, rgba(99, 102, 241, 0.22), transparent 55%),
    radial-gradient(ellipse 70% 45% at 100% 30%, rgba(14, 165, 233, 0.14), transparent 50%),
    radial-gradient(ellipse 55% 40% at 0% 75%, rgba(168, 85, 247, 0.12), transparent 48%),
    radial-gradient(ellipse 50% 35% at 85% 90%, rgba(56, 189, 248, 0.08), transparent 45%),
    radial-gradient(1px 1px at 8% 12%, rgba(255, 255, 255, 0.95), transparent),
    radial-gradient(1px 1px at 22% 8%, rgba(255, 255, 255, 0.75), transparent),
    radial-gradient(1px 1px at 35% 18%, rgba(255, 255, 255, 0.55), transparent),
    radial-gradient(1px 1px at 48% 6%, rgba(255, 255, 255, 0.85), transparent),
    radial-gradient(1px 1px at 62% 14%, rgba(255, 255, 255, 0.65), transparent),
    radial-gradient(1px 1px at 78% 22%, rgba(255, 255, 255, 0.9), transparent),
    radial-gradient(1px 1px at 92% 10%, rgba(255, 255, 255, 0.5), transparent),
    radial-gradient(1px 1px at 15% 35%, rgba(255, 255, 255, 0.7), transparent),
    radial-gradient(1px 1px at 88% 38%, rgba(255, 255, 255, 0.6), transparent),
    radial-gradient(1px 1px at 40% 42%, rgba(255, 255, 255, 0.45), transparent),
    radial-gradient(1px 1px at 55% 48%, rgba(255, 255, 255, 0.8), transparent),
    radial-gradient(1px 1px at 12% 58%, rgba(255, 255, 255, 0.55), transparent),
    radial-gradient(1px 1px at 72% 55%, rgba(255, 255, 255, 0.75), transparent),
    radial-gradient(1px 1px at 95% 62%, rgba(255, 255, 255, 0.5), transparent),
    radial-gradient(1px 1px at 28% 72%, rgba(255, 255, 255, 0.65), transparent),
    radial-gradient(1px 1px at 50% 78%, rgba(255, 255, 255, 0.4), transparent),
    radial-gradient(1px 1px at 65% 85%, rgba(255, 255, 255, 0.7), transparent),
    radial-gradient(1px 1px at 18% 88%, rgba(255, 255, 255, 0.55), transparent),
    radial-gradient(1px 1px at 82% 92%, rgba(255, 255, 255, 0.5), transparent),
    radial-gradient(1.5px 1.5px at 30% 28%, rgba(200, 230, 255, 0.9), transparent),
    radial-gradient(1.5px 1.5px at 70% 40%, rgba(200, 230, 255, 0.7), transparent);
  background-attachment: fixed;
}

.app {
  max-width: 1100px;
  margin: 0 auto;
  padding: 1.25rem 1rem 2rem;
}

.header {
  text-align: center;
  margin-bottom: 1rem;
}

.header h1 {
  margin: 0;
  font-size: clamp(1.5rem, 4vw, 2rem);
  color: #e0f2fe;
  text-shadow:
    0 0 24px rgba(56, 189, 248, 0.45),
    0 2px 8px rgba(0, 0, 0, 0.6);
  letter-spacing: 0.08em;
}

.subtitle {
  margin: 0.35rem 0 0;
  font-size: 0.9rem;
  color: var(--text-muted);
}

.controls {
  background: var(--panel);
  border: 1px solid var(--panel-border);
  border-radius: var(--radius);
  padding: 0.85rem 1rem;
  margin-bottom: 1rem;
  box-shadow:
    0 4px 24px rgba(0, 0, 0, 0.45),
    inset 0 1px 0 rgba(255, 255, 255, 0.06);
  backdrop-filter: blur(10px);
}

.control-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.75rem 1rem;
}

.control-row label {
  font-weight: 600;
}

.control-row--diff {
  align-items: flex-start;
}

.difficulty-field {
  margin: 0;
  padding: 0;
  border: none;
  min-width: 0;
}

.difficulty-legend {
  padding: 0;
  margin: 0 0 0.4rem;
  font-weight: 600;
  font-size: 0.9rem;
  color: var(--text-muted);
}

.diff-buttons {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
}

.diff-option {
  position: relative;
  cursor: pointer;
  margin: 0;
}

.diff-option input {
  position: absolute;
  opacity: 0;
  width: 0;
  height: 0;
  pointer-events: none;
}

.diff-option-label {
  display: inline-block;
  padding: 0.42rem 0.85rem;
  border-radius: 8px;
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--text-muted);
  background: rgba(15, 23, 42, 0.65);
  border: 1px solid rgba(100, 140, 200, 0.28);
  transition:
    color 0.15s ease,
    background 0.15s ease,
    border-color 0.15s ease,
    box-shadow 0.15s ease;
}

.diff-option:hover .diff-option-label {
  color: var(--text);
  border-color: rgba(148, 163, 184, 0.45);
}

.diff-option input:focus-visible + .diff-option-label {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.diff-option input:checked + .diff-option-label {
  color: #0a0e18;
  background: linear-gradient(165deg, var(--accent) 0%, var(--accent-dim) 100%);
  border-color: rgba(56, 189, 248, 0.55);
  box-shadow: 0 0 14px rgba(14, 165, 233, 0.35);
}

.btn {
  font: inherit;
  padding: 0.45rem 1rem;
  border-radius: 6px;
  border: none;
  cursor: pointer;
  transition: transform 0.08s ease, box-shadow 0.15s ease;
}

.btn:active {
  transform: scale(0.98);
}

.btn.primary {
  background: linear-gradient(165deg, var(--accent) 0%, var(--accent-dim) 100%);
  color: #0a0e18;
  font-weight: 600;
  box-shadow: 0 2px 14px rgba(14, 165, 233, 0.35);
}

.btn.primary:hover {
  filter: brightness(1.06);
}

.btn.secondary {
  background: rgba(30, 41, 59, 0.9);
  color: var(--text);
  border: 1px solid rgba(148, 163, 184, 0.35);
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.2);
}

.btn.secondary:hover:not(:disabled) {
  background: rgba(51, 65, 85, 0.95);
  border-color: rgba(186, 230, 253, 0.35);
}

.btn.secondary:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

.btn.ghost {
  background: transparent;
  color: var(--danger);
  border: 1px solid rgba(248, 113, 113, 0.4);
  margin-top: 0.75rem;
  width: 100%;
}

.btn.ghost:hover {
  background: rgba(248, 113, 113, 0.08);
}

.status-row {
  margin-top: 0.65rem;
  min-height: 1.5rem;
}

.status {
  margin: 0;
  font-weight: 600;
}

.thinking {
  margin: 0.25rem 0 0;
  font-size: 0.9rem;
  color: var(--text-muted);
  font-style: italic;
}

.thinking.hidden {
  display: none;
}

.main {
  display: flex;
  flex-wrap: wrap;
  gap: 1.25rem;
  align-items: flex-start;
  justify-content: center;
  position: relative;
}

.main::before {
  content: "";
  position: absolute;
  inset: -12px;
  z-index: -1;
  border-radius: calc(var(--radius) + 8px);
  background: radial-gradient(
    ellipse 70% 70% at 50% 50%,
    rgba(30, 58, 138, 0.25),
    transparent 70%
  );
  pointer-events: none;
}

.board {
  --cell-size: min(8vmin, 42px);
  display: grid;
  grid-template-columns: repeat(var(--cell-count), var(--cell-size));
  grid-template-rows: repeat(var(--cell-count), var(--cell-size));
  width: calc(var(--cell-count) * var(--cell-size));
  aspect-ratio: 1;
  position: relative;
  padding: calc(var(--cell-size) * 0.35);
  border-radius: calc(var(--radius) + 4px);
  background-color: var(--wood-mid);
  background-image:
    repeating-linear-gradient(
      90deg,
      transparent 0 2px,
      rgba(255, 255, 255, 0.03) 2px 4px
    ),
    repeating-linear-gradient(
      0deg,
      rgba(0, 0, 0, 0.06) 0 1px,
      transparent 1px 3px
    ),
    linear-gradient(
      105deg,
      var(--wood-dark) 0%,
      var(--wood-mid) 25%,
      var(--wood-light) 48%,
      var(--wood-mid) 72%,
      var(--wood-dark) 100%
    );
  box-shadow:
    inset 0 0 0 2px rgba(255, 255, 255, 0.12),
    inset 0 -8px 24px rgba(0, 0, 0, 0.25),
    0 12px 40px rgba(0, 0, 0, 0.45);
  border: 3px solid #3d2819;
}

.board::before {
  content: "";
  position: absolute;
  inset: calc(var(--cell-size) * 0.35);
  border-radius: 4px;
  background-image:
    linear-gradient(var(--grid-line) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid-line) 1px, transparent 1px);
  background-size:
    var(--cell-size) var(--cell-size),
    var(--cell-size) var(--cell-size);
  pointer-events: none;
  opacity: 0.95;
}

.cell {
  position: relative;
  z-index: 1;
  width: var(--cell-size);
  height: var(--cell-size);
  margin: 0;
  padding: 0;
  border: none;
  background: transparent;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
}

.cell:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
  border-radius: 4px;
}

.cell:not(.disabled):not(:disabled):hover .stone-placeholder {
  opacity: 0.35;
  transform: scale(1);
}

.cell.disabled,
.cell:disabled {
  cursor: default;
}

.stone-placeholder {
  width: calc(var(--cell-size) * 0.72);
  height: calc(var(--cell-size) * 0.72);
  border-radius: 50%;
  opacity: 0;
  transform: scale(0.85);
  transition: opacity 0.12s ease, transform 0.12s ease;
  pointer-events: none;
  background: radial-gradient(circle at 30% 28%, #444 0%, var(--black-stone) 45%, #000 100%);
  box-shadow: inset 0 -2px 4px rgba(255, 255, 255, 0.15);
}

.cell.black .stone,
.cell.white .stone {
  width: calc(var(--cell-size) * 0.72);
  height: calc(var(--cell-size) * 0.72);
  border-radius: 50%;
  pointer-events: none;
  position: relative;
}

.cell.black .stone {
  background: radial-gradient(circle at 32% 28%, #5a5a5a 0%, var(--black-stone) 35%, #0a0a0a 100%);
  box-shadow:
    0 2px 4px rgba(0, 0, 0, 0.5),
    inset 0 1px 2px rgba(255, 255, 255, 0.12);
}

.cell.white .stone {
  background: radial-gradient(circle at 32% 28%, #fff 0%, var(--white-stone) 45%, #d8d4cc 100%);
  box-shadow:
    0 2px 5px rgba(0, 0, 0, 0.35),
    inset 0 -1px 2px rgba(0, 0, 0, 0.08);
}

.cell.black.last-move .stone::after,
.cell.white.last-move .stone::after {
  content: "";
  position: absolute;
  inset: 35%;
  border-radius: 50%;
}

.cell.black.last-move .stone::after {
  background: rgba(255, 200, 80, 0.55);
  box-shadow: 0 0 6px rgba(255, 200, 80, 0.6);
}

.cell.white.last-move .stone::after {
  background: rgba(255, 120, 60, 0.45);
  box-shadow: 0 0 6px rgba(255, 120, 60, 0.5);
}

.stats-panel {
  background: var(--panel);
  border: 1px solid var(--panel-border);
  border-radius: var(--radius);
  padding: 1rem 1.15rem;
  min-width: 200px;
  box-shadow:
    0 4px 24px rgba(0, 0, 0, 0.45),
    inset 0 1px 0 rgba(255, 255, 255, 0.06);
  backdrop-filter: blur(10px);
}

.stats-panel h2 {
  margin: 0 0 0.65rem;
  font-size: 1.1rem;
  color: var(--panel-heading);
}

.stats-panel h3 {
  margin: 1rem 0 0.5rem;
  font-size: 0.95rem;
  color: var(--text-muted);
}

.stats-total,
.stats-current {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 0.35rem 1rem;
  margin: 0;
  font-size: 0.95rem;
}

.stats-total dt,
.stats-current dt {
  font-weight: 600;
  color: var(--text-muted);
}

.stats-total dd,
.stats-current dd {
  margin: 0;
  font-variant-numeric: tabular-nums;
}

@media (max-width: 640px) {
  .board {
    --cell-size: min(5.8vmin, 36px);
  }
}

.game-nav {
  margin-bottom: 0.35rem;
}

.nav-back {
  display: inline-block;
  font-size: 0.9rem;
  color: var(--accent);
  text-decoration: none;
  opacity: 0.9;
}

.nav-back:hover {
  text-decoration: underline;
  opacity: 1;
}