:root {
  --ink: #1d1f23;
  --muted: #5c616a;
  --accent: #e07a5f;
  --accent-strong: #c85a3b;
  --accent-glow: rgba(224, 122, 95, 0.12);
  --panel: #fff7ed;
  --panel-edge: #f0e6db;
  --demo-tab-bg: #fffdf8;
  --demo-tab-edge: #d4c7b8;
  --ttt-board: #f2e8dc;
  --ttt-cell: #fffaf4;
  --c4-board: #133d4a;
  --c4-hole: #0b2c36;
  --oth-board: #1f4f3d;
  --oth-cell: #2a6b4e;
  --oth-grid: rgba(14, 34, 26, 0.35);
  --oth-black: #0f0f12;
  --oth-white: #f2ede6;
  --oth-hint: rgba(240, 220, 180, 0.9);
  --p1: #d1495b;
  --p2: #f4d35e;
}

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

body {
  margin: 0;
  font-family: "DM Sans", "IBM Plex Sans", "Fira Sans", "Helvetica Neue", sans-serif;
  color: var(--ink);
  background: radial-gradient(1200px 600px at 15% 10%, #fff1e2 0%, transparent 60%),
    linear-gradient(135deg, #f7eee4 0%, #e7efe6 100%);
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

.app {
  max-width: 1120px;
  margin: 0 auto;
  padding: 32px 20px 60px;
}

header {
  position: relative;
  margin-bottom: 28px;
  animation: fadeSlideIn 0.5s ease both;
}

.mode-toggle {
  position: absolute;
  top: 0;
  right: 0;
  padding: 8px 14px;
  border-radius: 999px;
  border: 1px solid var(--demo-tab-edge);
  background: var(--demo-tab-bg);
  color: var(--muted);
  font-size: 0.8rem;
  font-weight: 600;
  text-decoration: none;
  white-space: nowrap;
  transition: transform 0.2s ease, color 0.2s ease, box-shadow 0.2s ease;
}

.mode-toggle:hover {
  transform: translateY(-1px);
  color: var(--accent-strong);
  box-shadow: 0 8px 16px rgba(40, 45, 55, 0.1);
}

.mode-toggle[hidden] {
  display: none;
}

.eyebrow {
  text-transform: uppercase;
  letter-spacing: 0.18em;
  font-size: 0.7rem;
  font-weight: 600;
  color: var(--accent);
  margin-bottom: 8px;
}

h1 {
  margin: 0 0 10px;
  font-family: "DM Serif Display", Georgia, serif;
  font-weight: 400;
  font-size: clamp(2rem, 4vw, 3rem);
  line-height: 1.15;
}

.title-brand {
  color: var(--accent-strong);
}

.title-sep {
  color: var(--panel-edge);
  font-weight: 300;
}

.subtitle {
  margin: 0;
  max-width: 620px;
  color: var(--muted);
  line-height: 1.5;
}

@keyframes fadeSlideIn {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}

.panel {
  background: var(--panel);
  border: 1px solid var(--panel-edge);
  border-radius: 16px;
  padding: 16px;
  box-shadow: 0 10px 30px rgba(30, 35, 40, 0.08);
  animation: fadeSlideIn 0.5s ease both;
  animation-delay: 0.08s;
}

.controls {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 12px;
  align-items: end;
}

@media (min-width: 960px) {
  .controls-files {
    grid-template-columns: repeat(2, minmax(180px, 1fr));
  }
  .controls-actions {
    grid-template-columns: auto auto 1fr;
  }
}

/* --- Per-player config panels --- */
.player-panels {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 12px;
  margin: 12px 0 8px;
  align-items: start;
}

@media (max-width: 640px) {
  .player-panels {
    grid-template-columns: 1fr;
  }
  .player-panels .swap-sides-btn {
    justify-self: center;
  }
}

.player-config {
  display: grid;
  gap: 8px;
  padding: 10px 12px;
  border: 1px solid var(--panel-edge);
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.5);
}

.player-header {
  font-weight: 600;
  font-size: 0.85rem;
  color: var(--ink);
  letter-spacing: 0.02em;
}

.swap-sides-btn {
  align-self: center;
  padding: 4px 8px;
  font-size: 1.2rem;
  line-height: 1;
  border: 1px solid var(--panel-edge);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.5);
  cursor: pointer;
  color: var(--ink);
  transition: background 0.15s;
}

.swap-sides-btn:hover:not(:disabled) {
  background: rgba(0, 0, 0, 0.06);
}

.swap-sides-btn:disabled {
  opacity: 0.4;
  cursor: default;
}

.player-config .model-params,
.player-config .heuristic-params {
  display: grid;
  gap: 6px;
}

.player-config .model-params[hidden],
.player-config .heuristic-params[hidden] {
  display: none;
}

/* --- Autoplay controls --- */
.autoplay-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  align-items: end;
  margin: 8px 0 4px;
  padding: 10px 12px;
  border: 1px solid var(--panel-edge);
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.5);
}

.autoplay-buttons {
  display: flex;
  gap: 6px;
}

.autoplay-buttons button {
  padding: 8px 12px;
  font-size: 0.85rem;
}

.autoplay-speed {
  min-width: 140px;
}

.autoplay-speed input[type="range"] {
  width: 100%;
}

.speed-value {
  font-variant-numeric: tabular-nums;
  font-size: 0.82rem;
  color: var(--muted);
}

.autoplay-batch {
  display: flex;
  gap: 6px;
  align-items: end;
}

.autoplay-batch input[type="number"] {
  width: 70px;
  padding: 8px;
  border-radius: 8px;
  border: 1px solid #dbcfc1;
  font-size: 0.9rem;
}

.batch-show-toggle {
  flex-direction: row;
  align-items: center;
  gap: 4px;
}

.autoplay-batch button {
  padding: 8px 14px;
  font-size: 0.85rem;
}

.batch-score {
  font-size: 0.88rem;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  color: var(--ink);
  min-width: 100px;
}

.batch-score:empty {
  display: none;
}

/* --- Graph player selector --- */
.graph-header-right {
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  gap: 4px;
}

/* Dashboard link in sweep info line */
.sweep-dash-link {
  color: var(--accent);
  text-decoration: none;
  font-weight: 500;
}
.sweep-dash-link:hover {
  text-decoration: underline;
}

/* Auto-loaded file indicator (replaces "no file chosen" for URL-loaded saves) */
.auto-loaded-name {
  display: block;
  font-size: 0.82rem;
  color: var(--accent);
  font-weight: 500;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

/* One-line "multi-core acceleration unavailable" notice (app.js showMultiCoreUnavailableNote). */
.mc-note {
  margin: 6px 0 0;
  font-size: 0.78rem;
  color: var(--muted);
  font-style: italic;
}

/* Engine capability indicator (#capabilities). Neutral/muted by default; green when the
   multi-threaded engine is active, warm-muted when single-threaded (see app.js). */
.capabilities {
  font-size: 0.78rem;
  color: var(--muted);
}
.capabilities.cap-threaded { color: #2e7d32; font-weight: 600; }
.capabilities.cap-single { color: var(--muted); }

#graphPlayerSelect {
  padding: 4px 8px;
  border-radius: 6px;
  border: 1px solid #dbcfc1;
  font-size: 0.82rem;
  background: #fff;
}

.control {
  display: grid;
  gap: 6px;
  min-width: 0;
  font-size: 0.85rem;
  color: var(--muted);
}

.control input,
.control select {
  padding: 10px 12px;
  width: 100%;
  box-sizing: border-box;
  border-radius: 10px;
  border: 1px solid #dbcfc1;
  background: #fff;
  font-size: 0.95rem;
  font-family: inherit;
  transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

.control input:focus,
.control select:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-glow);
}

.primary,
.secondary {
  padding: 12px 16px;
  border-radius: 12px;
  font-weight: 600;
  font-family: inherit;
  cursor: pointer;
  white-space: nowrap;
  align-self: end;
  transition: transform 0.2s ease, box-shadow 0.2s ease, background 0.2s ease;
}

.primary {
  border: none;
  background: var(--accent);
  color: #fff;
  letter-spacing: 0.02em;
}

.primary:disabled,
.secondary:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  box-shadow: none;
  transform: none;
}

.primary:not(:disabled):hover {
  transform: translateY(-1px);
  background: var(--accent-strong);
  box-shadow: 0 10px 20px rgba(224, 122, 95, 0.35);
}

.primary:not(:disabled):active {
  transform: translateY(0);
  box-shadow: 0 4px 10px rgba(224, 122, 95, 0.25);
}

.secondary {
  border: 1px solid #d4c7b8;
  background: #fffdf8;
  color: var(--ink);
}

.secondary:not(:disabled):hover {
  transform: translateY(-1px);
  box-shadow: 0 10px 20px rgba(40, 45, 55, 0.12);
}

.secondary:not(:disabled):active {
  transform: translateY(0);
  box-shadow: 0 4px 10px rgba(40, 45, 55, 0.08);
}

.meta {
  margin-top: 14px;
  padding-top: 12px;
  border-top: 1px solid var(--panel-edge);
  font-size: 0.88rem;
  display: grid;
  gap: 4px;
}

.meta-line {
  color: var(--muted);
  line-height: 1.45;
}

.meta-line:empty {
  display: none;
}

.status-area .meta-line:empty {
  display: block;
}

.meta-line.score {
  color: var(--ink);
  font-weight: 600;
  letter-spacing: 0.02em;
  font-variant-numeric: tabular-nums;
}

.training-params {
  font-size: 0.82rem;
  font-variant-numeric: tabular-nums;
}

.error {
  color: #b0413e;
  font-weight: 500;
}

.meta-line.status-busy {
  color: var(--accent);
  font-weight: 600;
  animation: statusPulse 1.5s ease-in-out infinite;
}

@keyframes statusPulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.6; }
}

.status-area {
  display: grid;
  grid-template-rows: auto 1.3em;   /* history block (reserved below) + current line */
}

/* Rolling status history: reserve space for kStatusHistoryLen rows so height is stable, newest at
   the bottom hugging the current line. */
.status-history {
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  min-height: calc(3 * 1.15em);
}

.status-hist {
  font-size: 0.85em;
  line-height: 1.15em;
  opacity: 0.45;
}
.status-hist:last-child { opacity: 0.7; }   /* most-recent history line a touch brighter */

main {
  margin-top: 28px;
  display: grid;
  gap: 24px;
}

main > .panel {
  opacity: 0;
  animation: fadeSlideIn 0.5s ease forwards;
}

@media (min-width: 980px) {
  main {
    grid-template-columns: minmax(540px, 1fr) minmax(360px, 1fr);
    align-items: start;
  }
}

.board-panel {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  animation-delay: 0.15s;
}

.graph-panel {
  animation-delay: 0.22s;
}

.board {
  display: grid;
  gap: 8px;
  padding: 16px;
  border-radius: 18px;
  min-width: 240px;
  max-width: min(90vw, 540px);
  width: 100%;
}

.graph-panel {
  display: grid;
  gap: 12px;
}

.graph-header {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 12px;
  align-items: center;
}

.graph-header h2 {
  margin: 0 0 6px;
  font-family: "DM Serif Display", Georgia, serif;
  font-weight: 400;
  font-size: 1.2rem;
}

.graph-subtitle {
  margin: 0;
  color: var(--muted);
  font-size: 0.85rem;
}

.graph-stats {
  color: var(--muted);
  font-size: 0.9rem;
}

.transcript-panel {
  display: grid;
  gap: 12px;
  animation-delay: 0.3s;
}

@media (min-width: 980px) {
  .transcript-panel {
    grid-column: 1 / -1;
  }
}

.transcript-header {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 12px;
  align-items: flex-start;
}

.transcript-header h2 {
  margin: 0 0 6px;
  font-family: "DM Serif Display", Georgia, serif;
  font-weight: 400;
  font-size: 1.2rem;
}

.transcript-subtitle {
  margin: 0;
  color: var(--muted);
  font-size: 0.85rem;
}

.transcript-actions {
  display: flex;
  gap: 8px;
  flex-shrink: 0;
}

.transcript-text {
  margin: 0;
  max-height: 420px;
  overflow: auto;
  padding: 12px 14px;
  border-radius: 12px;
  background: #fffdf8;
  border: 1px solid var(--panel-edge);
  color: var(--ink);
  font-family: "SFMono-Regular", "Fira Code", "Consolas", ui-monospace, monospace;
  font-size: 0.8rem;
  line-height: 1.4;
  white-space: pre;
  tab-size: 2;
  user-select: text;
}

.graph-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
  align-items: center;
}

.graph-mode {
  min-width: 200px;
}

.graph-tooltip {
  position: fixed;
  left: 0;
  top: 0;
  transform: translate3d(0, 0, 0);
  pointer-events: none;
  z-index: 1000;
  opacity: 0;
  transition: opacity 0.08s ease;
  background: rgba(20, 22, 26, 0.92);
  color: #f7f1e9;
  border: 1px solid rgba(255, 255, 255, 0.12);
  border-radius: 12px;
  padding: 8px 10px;
  font-size: 0.78rem;
  line-height: 1.25;
  box-shadow: 0 12px 30px rgba(10, 12, 14, 0.25);
  max-width: min(70vw, 320px);
}

.graph-tooltip.visible {
  opacity: 1;
}

.control.compact {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 10px;
  font-size: 0.8rem;
}

.control.compact input[type="range"] {
  width: 160px;
}

input[type="range"] {
  -webkit-appearance: none;
  appearance: none;
  background: transparent;
  cursor: pointer;
}

input[type="range"]::-webkit-slider-runnable-track {
  height: 6px;
  background: var(--panel-edge);
  border-radius: 3px;
}

input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 16px;
  height: 16px;
  background: var(--accent);
  border-radius: 50%;
  margin-top: -5px;
}

input[type="range"]::-moz-range-track {
  height: 6px;
  background: var(--panel-edge);
  border-radius: 3px;
  border: none;
}

input[type="range"]::-moz-range-thumb {
  width: 16px;
  height: 16px;
  background: var(--accent);
  border-radius: 50%;
  border: none;
}

.graph-value {
  font-variant-numeric: tabular-nums;
  color: var(--ink);
}

.toggle {
  display: inline-flex;
  gap: 8px;
  align-items: center;
  font-size: 0.85rem;
  color: var(--muted);
}

.graph-canvas {
  border-radius: 14px;
  border: 1px solid var(--panel-edge);
  background: linear-gradient(180deg, #fffdf8 0%, #faf5ee 100%);
  padding: 12px;
  min-height: 320px;
}

.graph-canvas canvas {
  width: 100%;
  height: 360px;
  display: block;
}

.board.ttt {
  background: var(--ttt-board);
  box-shadow: inset 0 0 0 2px rgba(80, 70, 60, 0.08);
}

.board.c4 {
  background: var(--c4-board);
  box-shadow: inset 0 0 0 2px rgba(5, 20, 24, 0.35);
}

.board.oth {
  background: var(--oth-board);
  box-shadow: inset 0 0 0 2px var(--oth-grid);
  gap: 6px;
}

.cell {
  aspect-ratio: 1 / 1;
  display: grid;
  place-items: center;
  font-size: clamp(1.6rem, 6vw, 2.8rem);
  font-weight: 600;
  color: var(--ink);
  background: var(--ttt-cell);
  border-radius: 12px;
  cursor: pointer;
  position: relative;
  transition: transform 0.15s ease, box-shadow 0.2s ease;
}

.cell.win {
  animation: winPulse 0.9s ease-in-out 0s 4;
  outline: 2px solid var(--accent-strong);
  outline-offset: -4px;
}

.board.hex .cell.win {
  outline: none;
  z-index: 1200 !important;
}

.board.c4 .cell.win {
  outline: 3px solid #f6bd60;
  outline-offset: -6px;
}

.board.c4 .cell {
  background: var(--c4-hole);
  border-radius: 50%;
  box-shadow: inset 0 2px 6px rgba(0, 0, 0, 0.4);
  font-size: 0;
}

.board.oth .cell {
  background: linear-gradient(135deg, rgba(255, 255, 255, 0.06), rgba(0, 0, 0, 0.08)),
    var(--oth-cell);
  border-radius: 10px;
  box-shadow: inset 0 0 0 1px var(--oth-grid);
  font-size: 0;
}

.board.oth .cell::before {
  content: "";
  position: absolute;
  width: 24%;
  height: 24%;
  border-radius: 50%;
  background: var(--oth-hint);
  opacity: 0;
  transform: scale(0.6);
  transition: opacity 0.15s ease, transform 0.2s ease;
  box-shadow: 0 0 10px rgba(245, 236, 215, 0.35);
}

.board.oth .cell.legal::before {
  opacity: 1;
  transform: scale(1);
}

.board.oth .cell::after {
  content: "";
  position: absolute;
  width: 72%;
  height: 72%;
  border-radius: 50%;
  opacity: 0;
  transform: scale(0.2);
  transition: opacity 0.15s ease, transform 0.2s ease;
  box-shadow: inset 0 2px 6px rgba(0, 0, 0, 0.35), 0 6px 12px rgba(0, 0, 0, 0.25);
}

.board.oth .cell.p1::after {
  opacity: 1;
  transform: scale(1);
  background: radial-gradient(circle at 30% 30%, #4b4c53, var(--oth-black));
}

.board.oth .cell.p2::after {
  opacity: 1;
  transform: scale(1);
  background: radial-gradient(circle at 30% 30%, #ffffff, var(--oth-white));
}

.cell:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 18px rgba(30, 35, 40, 0.18);
}

.cell.p1 {
  color: var(--p1);
}

.cell.p2 {
  color: #355070;
}

.board.c4 .cell.p1,
.board.c4 .cell.p2 {
  box-shadow: inset 0 2px 8px rgba(0, 0, 0, 0.45), 0 6px 16px rgba(0, 0, 0, 0.2);
}

.board.c4 .cell.p1 {
  background: radial-gradient(circle at 30% 30%, #f7b2b8, var(--p1));
}

.board.c4 .cell.p2 {
  background: radial-gradient(circle at 30% 30%, #fff3b0, var(--p2));
}

@media (max-width: 640px) {
  .app {
    padding: 24px 16px 40px;
  }

  .controls {
    grid-template-columns: 1fr;
  }

  .control.compact input[type="range"] {
    width: 100%;
  }
}

@keyframes winPulse {
  0% {
    transform: scale(1);
    box-shadow: 0 0 0 rgba(224, 122, 95, 0.0);
  }
  50% {
    transform: scale(1.05);
    box-shadow: 0 0 18px rgba(224, 122, 95, 0.35);
  }
  100% {
    transform: scale(1);
    box-shadow: 0 0 0 rgba(224, 122, 95, 0.0);
  }
}

/* Othello score bars */
.othello-score-bars {
  display: none;
  width: 100%;
  max-width: min(90vw, 540px);
  margin-top: 16px;
  padding: 12px 16px;
  background: var(--oth-board);
  border-radius: 12px;
  box-shadow: inset 0 0 0 2px var(--oth-grid);
}

.othello-score-bars.visible {
  display: block;
}

.score-row {
  display: grid;
  grid-template-columns: 50px 1fr 36px;
  align-items: center;
  gap: 12px;
  margin-bottom: 8px;
}

.score-row:last-of-type {
  margin-bottom: 0;
}

.score-label {
  font-size: 0.85rem;
  font-weight: 600;
  color: rgba(255, 255, 255, 0.85);
}

.score-bar-container {
  height: 20px;
  background: rgba(0, 0, 0, 0.25);
  border-radius: 10px;
  overflow: hidden;
}

.score-bar {
  height: 100%;
  border-radius: 10px;
  transition: width 0.3s ease;
}

.score-bar.black-bar {
  background: radial-gradient(ellipse at 30% 30%, #4b4c53, var(--oth-black));
  box-shadow: inset 0 1px 3px rgba(255, 255, 255, 0.15);
}

.score-bar.white-bar {
  background: radial-gradient(ellipse at 30% 30%, #ffffff, var(--oth-white));
  box-shadow: inset 0 -1px 3px rgba(0, 0, 0, 0.1);
}

.score-count {
  font-size: 0.9rem;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  text-align: right;
  color: rgba(255, 255, 255, 0.95);
}

.winner-display {
  margin-top: 10px;
  text-align: center;
  font-size: 1rem;
  font-weight: 700;
  color: var(--oth-hint);
  min-height: 1.2em;
}

.winner-display:empty {
  display: none;
}

.winner-display.black-wins {
  color: #a0a0a8;
}

.winner-display.white-wins {
  color: var(--oth-white);
}

/* Gomoku board styling — Go-style intersection grid with round stones */
.board.gomoku {
  background: #DCB468;
  gap: 0;
  padding: 12px;
  border-radius: 12px;
  box-shadow:
    inset 0 1px 0 rgba(255, 255, 255, 0.15),
    0 6px 24px rgba(0, 0, 0, 0.18);
}

.board.gomoku .cell {
  background: transparent;
  border: none;
  border-radius: 0;
  position: relative;
  font-size: 0;
  cursor: pointer;
  transition: none;
}

.board.gomoku .cell:hover {
  transform: none;
  box-shadow: none;
}

/* Grid lines through cell centers — four half-line layers anchored from center to each edge */
.board.gomoku .cell::before {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  --gk-line: rgba(0, 0, 0, 0.55);
  background:
    linear-gradient(var(--gk-line), var(--gk-line)) right 0 top 50%  / 50% 1px no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 0 top 50%   / 50% 1px no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 50% bottom 0 / 1px 50% no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 50% top 0    / 1px 50% no-repeat;
}

/* Edge cells: drop the outward-facing half-line */
.board.gomoku .cell.gk-left::before {
  background:
    linear-gradient(var(--gk-line), var(--gk-line)) right 0 top 50%  / 50% 1px no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 50% bottom 0 / 1px 50% no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 50% top 0    / 1px 50% no-repeat;
}
.board.gomoku .cell.gk-right::before {
  background:
    linear-gradient(var(--gk-line), var(--gk-line)) left 0 top 50%   / 50% 1px no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 50% bottom 0 / 1px 50% no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 50% top 0    / 1px 50% no-repeat;
}
.board.gomoku .cell.gk-top::before {
  background:
    linear-gradient(var(--gk-line), var(--gk-line)) right 0 top 50%  / 50% 1px no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 0 top 50%   / 50% 1px no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 50% bottom 0 / 1px 50% no-repeat;
}
.board.gomoku .cell.gk-bottom::before {
  background:
    linear-gradient(var(--gk-line), var(--gk-line)) right 0 top 50%  / 50% 1px no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 0 top 50%   / 50% 1px no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 50% top 0    / 1px 50% no-repeat;
}
/* Corners: only two inward-facing half-lines */
.board.gomoku .cell.gk-top.gk-left::before {
  background:
    linear-gradient(var(--gk-line), var(--gk-line)) right 0 top 50%  / 50% 1px no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 50% bottom 0 / 1px 50% no-repeat;
}
.board.gomoku .cell.gk-top.gk-right::before {
  background:
    linear-gradient(var(--gk-line), var(--gk-line)) left 0 top 50%   / 50% 1px no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 50% bottom 0 / 1px 50% no-repeat;
}
.board.gomoku .cell.gk-bottom.gk-left::before {
  background:
    linear-gradient(var(--gk-line), var(--gk-line)) right 0 top 50%  / 50% 1px no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 50% top 0    / 1px 50% no-repeat;
}
.board.gomoku .cell.gk-bottom.gk-right::before {
  background:
    linear-gradient(var(--gk-line), var(--gk-line)) left 0 top 50%   / 50% 1px no-repeat,
    linear-gradient(var(--gk-line), var(--gk-line)) left 50% top 0    / 1px 50% no-repeat;
}

/* Star points (hoshi) */
.board.gomoku .cell.gk-star::after {
  content: "";
  position: absolute;
  width: 18%;
  height: 18%;
  min-width: 5px;
  min-height: 5px;
  border-radius: 50%;
  background: rgba(0, 0, 0, 0.6);
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  z-index: 1;
  pointer-events: none;
}

/* Stones — drawn via ::after pseudo-element */
.board.gomoku .cell.p1::after,
.board.gomoku .cell.p2::after {
  content: "";
  position: absolute;
  width: 88%;
  height: 88%;
  border-radius: 50%;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  z-index: 2;
  pointer-events: none;
}

/* Black stone */
.board.gomoku .cell.p1::after {
  background: radial-gradient(circle at 36% 36%, #606060, #222 45%, #0a0a0a);
  box-shadow:
    inset 0 -1px 3px rgba(255, 255, 255, 0.08),
    1px 2px 4px rgba(0, 0, 0, 0.45);
}

/* White stone */
.board.gomoku .cell.p2::after {
  background: radial-gradient(circle at 36% 36%, #ffffff, #f0f0f0 40%, #d8d8d8);
  box-shadow:
    inset 0 -1px 3px rgba(0, 0, 0, 0.06),
    1px 2px 4px rgba(0, 0, 0, 0.3);
  border: 1px solid rgba(0, 0, 0, 0.18);
}

/* Hover ghost preview for empty cells */
.board.gomoku .cell:not(.p1):not(.p2):hover::after {
  content: "";
  position: absolute;
  width: 88%;
  height: 88%;
  border-radius: 50%;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  z-index: 2;
  pointer-events: none;
  background: rgba(0, 0, 0, 0.15);
}

/* Win highlight */
.board.gomoku .cell.win {
  outline: none;
}

.board.gomoku .cell.win::after {
  filter: drop-shadow(0 0 6px #ffd700) drop-shadow(0 0 12px rgba(255, 215, 0, 0.5));
  animation: gomokuWinPulse 1s ease-in-out infinite;
}

@keyframes gomokuWinPulse {
  0%, 100% { filter: drop-shadow(0 0 6px #ffd700) drop-shadow(0 0 12px rgba(255, 215, 0, 0.5)); }
  50% { filter: drop-shadow(0 0 10px #ffd700) drop-shadow(0 0 20px rgba(255, 215, 0, 0.6)) brightness(1.1); }
}

/* Hex board styling */
:root {
  --hex-board: #fdf6e3;
  --hex-cell: #ffffff;
  --hex-p1: #d14545;  /* Red */
  --hex-p2: #3a7bd5;  /* Blue */
  --hex-grid: #000000;
  --hex-gold: #f6bd60;
}

.board.hex {
  background: var(--hex-board);
  border: none;
  border-radius: 20px;
  box-shadow: 0 14px 40px rgba(0, 0, 0, 0.1);
  padding: 0;
  gap: 0;
  position: relative;
  max-width: none;
  width: auto;
  overflow: visible; 
  border: 1px solid rgba(0, 0, 0, 0.05);
}

.hex-label {
  position: absolute;
  font-family: 'Inter', 'Segoe UI', system-ui, sans-serif;
  font-weight: 900;
  font-size: 18px;
  pointer-events: none;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  transform: translate(-50%, -50%);
  text-shadow: 0 1px 2px rgba(0,0,0,0.05);
  z-index: 200;
}

.hex-label-top, .hex-label-bottom { color: var(--hex-p1); }
.hex-label-left, .hex-label-right { color: var(--hex-p2); }

.board.hex .cell {
  width: var(--hex-w);
  height: var(--hex-h);
  position: absolute;
  background: transparent;
  transition: transform 0.14s ease;
  cursor: pointer;
}

.board.hex .cell:hover {
  z-index: 1000 !important;
  transform: scale(1.05);
}

/* Hex Outline - Black background for 1px gap outline */
.board.hex .cell::before {
  content: "";
  position: absolute;
  inset: 0;
  clip-path: polygon(50% 0%, 100% 25%, 100% 75%, 50% 100%, 0% 75%, 0% 25%);
  background: var(--hex-grid);
  pointer-events: none;
  z-index: 1;
}

/* Empty Cell Fill - Use board cell color to show only the black outline */
.board.hex .cell .hex-tile {
  position: absolute;
  inset: 1px;
  clip-path: polygon(50% 0%, 100% 25%, 100% 75%, 50% 100%, 0% 75%, 0% 25%);
  background: var(--hex-cell);
  pointer-events: none;
  z-index: 2;
  transition: background 0.2s ease;
}

.board.hex .cell:hover .hex-tile {
  background: rgba(0, 0, 0, 0.05);
}

/* Player Pieces - Direct red/blue fill */
.board.hex .cell.p1 .hex-tile {
  background: var(--hex-p1);
}

.board.hex .cell.p2 .hex-tile {
  background: var(--hex-p2);
}

/* Win Highlight: Glow effect on winning cells */
.board.hex .cell.win .hex-tile {
  filter: drop-shadow(0 0 8px #ffd700) drop-shadow(0 0 16px rgba(255, 215, 0, 0.4));
  animation: hexWinPulse 1.2s ease-in-out infinite;
  z-index: 10;
}

@keyframes hexWinPulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.08); filter: brightness(1.2); }
}

/* Goal Markers: Solid continuous zig-zag for Red, sharp pointers for Blue */
.board.hex .cell.edge-top .hex-edge-tb {
  top: -22%;
  left: -18%;
  right: -15%;
  height: 45%;
  background: var(--hex-p1);
  clip-path: polygon(50% 0%, 100% 50%, 50% 100%, 0% 50%); /* Interlocking diamond */
}

.board.hex .cell.edge-bottom .hex-edge-tb {
  bottom: -22%;
  left: -15%;
  right: -18%;
  height: 45%;
  background: var(--hex-p1);
  clip-path: polygon(50% 100%, 100% 50%, 50% 0%, 0% 50%); /* Interlocking diamond */
}

.board.hex .cell.edge-left .hex-edge-lr {
  left: -30%;
  top: 10%;
  bottom: 10%;
  width: 35%;
  background: var(--hex-p2);
  clip-path: polygon(100% 50%, 0% 10%, 0% 90%); /* Inward sharp pointer */
}

.board.hex .cell.edge-right .hex-edge-lr {
  right: -30%;
  top: 10%;
  bottom: 10%;
  width: 35%;
  background: var(--hex-p2);
  clip-path: polygon(0% 50%, 100% 10%, 100% 90%); /* Inward sharp pointer */
}

/* Hover Ghost Preview */
.board.hex[data-hex-preview="1"] .cell:not(.p1):not(.p2):hover .hex-tile {
  background: rgba(209, 69, 69, 0.3);
  inset: 0;
}

.board.hex[data-hex-preview="2"] .cell:not(.p1):not(.p2):hover .hex-tile {
  background: rgba(58, 123, 213, 0.3);
  inset: 0;
}

/* Sweep CSV rank buttons */
.sweep-info {
  display: flex;
  align-items: center;
  gap: 6px;
  flex-wrap: wrap;
  font-size: 0.84rem;
}

.sweep-rank-btn {
  display: inline-block;
  padding: 3px 10px;
  border-radius: 8px;
  border: 1px solid #d4c7b8;
  background: #fffdf8;
  color: var(--ink);
  font-size: 0.8rem;
  font-weight: 600;
  font-family: inherit;
  cursor: pointer;
  transition: background 0.15s ease, border-color 0.15s ease, transform 0.15s ease, box-shadow 0.15s ease;
  font-variant-numeric: tabular-nums;
}

.sweep-rank-btn:hover {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(224, 122, 95, 0.3);
}

.sweep-rank-btn:active {
  transform: translateY(0);
  box-shadow: 0 2px 6px rgba(224, 122, 95, 0.2);
}

/* Responsive */
@media (max-width: 640px) {
  .board.hex { padding: 12px; }
  .board.hex .cell { width: var(--hex-w); height: var(--hex-h); }
}

/* =================================================================================================
   Web-play demo (docs/PLAN-webui-demo-fbf243.md §7 Phase 3). Injected by web/demo.js only under
   ?demo=1 — the tab strip + blurb + the Advanced disclosure that de-emphasizes the dev-only pickers.
   Fonts: the display heading + body already carry non-CDN fallback stacks (DM Serif Display/DM Sans
   are SELF-HOSTED via dm-fonts.css, no Google-Fonts <link>), so no separate system-font stack is
   added here (§4.1 — reconciled with the companion self-host).
   ================================================================================================= */

/* Tab strip — reuses the existing accent/panel palette; keyboard-focusable, hover + active states. */
.demo-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 18px 0 10px;
}

.demo-tab {
  padding: 8px 16px;
  border: 1px solid var(--demo-tab-edge);
  border-radius: 999px;
  background: var(--demo-tab-bg);
  color: var(--muted);
  font-family: inherit;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.15s ease, box-shadow 0.15s ease, background 0.15s ease, color 0.15s ease;
}

.demo-tab:hover {
  transform: translateY(-1px);
  color: var(--ink);
  box-shadow: 0 8px 18px rgba(40, 45, 55, 0.12);
}

.demo-tab:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 2px;
}

.demo-tab.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
  box-shadow: 0 6px 16px rgba(224, 122, 95, 0.32);
}

.demo-blurb {
  margin: 0 0 4px;
  max-width: 620px;
  min-height: 1.4em; /* reserve a line so the layout doesn't jump between load states */
  color: var(--muted);
  line-height: 1.5;
}

.demo-blurb.loading { font-style: italic; }

.demo-blurb.error {
  color: var(--accent-strong);
  font-weight: 600;
}

/* Advanced disclosure — collapses the dev-only file pickers (Save file / checkpoints / Sweep CSV). */
details.advanced {
  margin-bottom: 8px;
  border: 1px dashed var(--panel-edge);
  border-radius: 12px;
  padding: 6px 12px;
  background: rgba(255, 253, 248, 0.6);
}

details.advanced > summary {
  cursor: pointer;
  color: var(--muted);
  font-size: 0.85rem;
  font-weight: 600;
  letter-spacing: 0.02em;
  padding: 4px 0;
  list-style: none;
}

details.advanced > summary::-webkit-details-marker { display: none; }

details.advanced > summary::before {
  content: "▸ ";
  color: var(--accent);
}

details.advanced[open] > summary::before { content: "▾ "; }

details.advanced > summary:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 2px;
  border-radius: 6px;
}

details.advanced > .controls-files {
  margin-top: 10px;
}