/* Simpler visual layer: keeps all game behavior and controls intact. */
:root {
  --surface-soft: #f7f7f7;
  --line: #d8d8d8;
  --line-strong: #bdbdbd;
  --shadow: none;
  --shadow-soft: none;
  --radius-xl: 12px;
  --radius-lg: 10px;
  --radius-md: 8px;
  --radius-sm: 6px;
}

body {
  background: #f3f3f3;
}

.site-header {
  align-items: center;
  padding-top: 24px;
  padding-bottom: 18px;
}

.site-header h1 {
  font-size: clamp(2rem, 5vw, 3.4rem);
  letter-spacing: -0.04em;
}

.eyebrow,
.header-copy {
  display: none;
}

.header-link {
  padding: 8px 12px;
  color: var(--ink);
  background: transparent;
  border: 1px solid var(--line-strong);
  border-radius: 7px;
  box-shadow: none;
}

.game-layout {
  gap: 16px;
}

.game-card,
.control-card,
.rules-section,
.formalization-section {
  background: #fff;
  border: 1px solid var(--line);
  box-shadow: none;
}

.game-card,
.control-card {
  border-radius: 12px;
}

.toolbar {
  padding: 12px 14px;
  background: #fff;
  border-bottom: 1px solid var(--line);
}

.toolbar .checker-stepper {
  color: var(--ink);
  background: var(--surface-soft);
  border-color: var(--line);
}

.button,
.icon-button {
  border-radius: 7px;
  box-shadow: none !important;
  transform: none !important;
}

.button-primary {
  color: #fff;
  background: var(--navy);
  border-color: var(--navy);
}

.score-strip {
  background: #fff;
}

.score-strip > div {
  padding: 10px 14px;
}

.play-area {
  gap: 14px;
  padding: 22px;
}

.bin-panel {
  padding: 12px 8px;
  border-radius: 9px;
  background: #fafafa;
}

.blue-bin-panel,
.red-bin-panel {
  background: #fafafa;
}

.bin-piece {
  width: 58px;
  height: 58px;
  box-shadow: none;
}

.bin-piece.blue {
  background: var(--blue);
}

.bin-piece.red {
  background: var(--red);
}

.mini-piece,
.checker {
  box-shadow: none;
}

.checker.blue {
  background: var(--blue);
}

.checker.red {
  background: var(--red);
}

.board {
  border: 2px solid var(--navy);
  border-radius: 6px;
  box-shadow: none;
}

.board-cell,
.board-cell:nth-child(16n + 1),
.board-cell:nth-child(16n + 3),
.board-cell:nth-child(16n + 5),
.board-cell:nth-child(16n + 7),
.board-cell:nth-child(16n + 10),
.board-cell:nth-child(16n + 12),
.board-cell:nth-child(16n + 14),
.board-cell:nth-child(16n + 16) {
  background: #fff;
}

.board-cell:nth-child(16n + 1),
.board-cell:nth-child(16n + 3),
.board-cell:nth-child(16n + 5),
.board-cell:nth-child(16n + 7),
.board-cell:nth-child(16n + 10),
.board-cell:nth-child(16n + 12),
.board-cell:nth-child(16n + 14),
.board-cell:nth-child(16n + 16) {
  background: #f1f1f1;
}

.interaction-hint {
  margin-top: 8px;
}

.move-history {
  padding: 0 18px 18px;
}

.history-list {
  padding: 8px;
  background: #fff;
  border-radius: 7px;
}

.history-list li {
  border-radius: 5px;
}

.control-section {
  padding: 15px;
}

.choice-card,
.nested-options,
.warning-note {
  border-radius: 7px;
}

.choice-card:has(input:checked) {
  background: #eef4ff;
}

.proof-card {
  background: #fff;
}

.rules-section,
.formalization-section {
  margin-top: 18px;
  padding: 24px;
  border-radius: 12px;
}

.rules-section > h2,
.formalization-section > h2 {
  margin-bottom: 16px;
  font-size: clamp(1.5rem, 3vw, 2.2rem);
}

.rules-grid,
.proof-steps {
  gap: 10px;
}

.rules-grid article,
.proof-steps article {
  padding: 14px;
  background: #fff;
  border-radius: 7px;
}

.proof-steps article > span {
  width: 32px;
  height: 32px;
  border-radius: 6px;
}

footer {
  padding-bottom: 24px;
}

@media (max-width: 640px) {
  .site-header {
    padding-top: 18px;
  }

  .game-card,
  .control-card,
  .rules-section,
  .formalization-section {
    border-radius: 10px;
  }

  .play-area {
    padding: 14px 8px 20px;
  }
}