:root {
  --bg: #eef2f7;
  --panel: #ffffff;
  --ink: #1a2433;
  --muted: #6a7588;
  --accent: #0f766e;
  --p1: #ea580c;
  --p2: #2563eb;
  --line: #d7deea;
  --win: #f59e0b;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Avenir Next", "Segoe UI", sans-serif;
  color: var(--ink);
  min-height: 100vh;
  background:
    radial-gradient(circle at 20% 15%, #ffffff, transparent 48%),
    linear-gradient(145deg, #edf4ff 0%, #e9f6ef 55%, #f4efe6 100%);
}

.app {
  display: grid;
  grid-template-columns: minmax(280px, 360px) 1fr;
  gap: 18px;
  padding: 18px;
}

.panel {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 14px;
  box-shadow: 0 10px 24px rgba(29, 44, 77, 0.08);
}

.setup-screen {
  min-height: 100vh;
  display: grid;
  place-items: center;
  padding: 18px;
}

.setup-card {
  width: min(540px, 100%);
  padding: 20px;
}

.start-btn {
  width: 100%;
  height: 42px;
  font-weight: 600;
}

.game-screen {
  min-height: 100vh;
}

.game-topbar {
  position: fixed;
  top: 12px;
  left: 12px;
  right: 12px;
  z-index: 30;
  display: flex;
  justify-content: space-between;
  gap: 8px;
  pointer-events: none;
}

.game-topbar button {
  pointer-events: auto;
  box-shadow: 0 8px 20px rgba(29, 44, 77, 0.15);
}

.app.game-fullscreen {
  grid-template-columns: 1fr;
  gap: 0;
  padding: 0;
  min-height: 100vh;
}

.app.game-fullscreen .board-panel {
  border-radius: 0;
  border: none;
  box-shadow: none;
  min-height: 100vh;
  height: 100vh;
  padding: 0;
}

.app.game-fullscreen .board-container {
  min-height: 100vh;
  padding: 56px 12px 12px;
}

.app.game-controls-hidden .controls {
  display: none;
}

.app.game-fullscreen .controls {
  position: fixed;
  z-index: 25;
  top: 60px;
  left: 12px;
  bottom: 12px;
  width: min(360px, calc(100vw - 24px));
  overflow: auto;
}

.controls {
  padding: 16px;
}

h1 {
  margin: 0;
  font-size: 1.45rem;
}

.subtitle {
  margin-top: 6px;
  margin-bottom: 14px;
  color: var(--muted);
}

.control-group {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin-bottom: 14px;
}

.slider-group {
  display: flex;
  align-items: center;
  gap: 8px;
}

.slider-group span {
  min-width: 72px;
  font-size: 0.88rem;
  color: var(--muted);
}

.toggle-row {
  display: flex;
  align-items: center;
  gap: 8px;
  cursor: pointer;
  color: var(--ink);
}

.toggle-row input[type="checkbox"] {
  width: 16px;
  height: 16px;
  padding: 0;
  border-radius: 4px;
}

.hint-text {
  font-size: 0.86rem;
  color: var(--muted);
}

.row {
  flex-direction: row;
}

label {
  font-size: 0.9rem;
  color: var(--muted);
}

input,
button {
  height: 38px;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 0 10px;
  font-size: 0.95rem;
}

button {
  cursor: pointer;
  background: #f9fafb;
  color: var(--ink);
  transition: transform 120ms ease, background 120ms ease;
}

button:hover {
  background: #edf2f8;
}

button:active {
  transform: translateY(1px);
}

.mode-buttons {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
}

.mode-btn.active {
  border-color: var(--accent);
  color: #0b5c55;
  background: #def7f3;
}

.hidden {
  display: none;
}

.status-box {
  border: 1px dashed var(--line);
  border-radius: 10px;
  padding: 10px;
  min-height: 72px;
}

#turnText {
  font-weight: 600;
}

#messageText {
  margin-top: 4px;
  color: var(--muted);
}

.legend {
  margin-top: 12px;
  display: flex;
  flex-direction: column;
  gap: 6px;
  font-size: 0.92rem;
}

.dot {
  display: inline-block;
  width: 12px;
  height: 12px;
  border-radius: 999px;
  margin-right: 6px;
}

.dot.p1 {
  background: var(--p1);
}

.dot.p2 {
  background: var(--p2);
}

.board-panel {
  padding: 16px;
  overflow: auto;
  min-height: calc(100vh - 36px);
}

.board-container {
  perspective: 1000px;
  transform-style: preserve-3d;
  padding: 12px;
  min-height: calc(100vh - 72px);
  display: grid;
  place-items: center;
  cursor: grab;
  user-select: none;
  touch-action: none;
  overscroll-behavior: contain;
}

.board-container.dragging {
  cursor: grabbing;
}

.layers {
  position: relative;
  width: max-content;
  margin: 20px auto;
  transform: translateY(var(--board-shift-y, 110px))
    translateZ(var(--camera-z, 120px)) rotateX(var(--rot-x, 58deg))
    rotateZ(var(--rot-z, -34deg));
  transform-style: preserve-3d;
  animation: enter 360ms ease;
}

@keyframes enter {
  from {
    opacity: 0;
    transform: translateY(var(--board-shift-y, 110px))
      translateZ(calc(var(--camera-z, 120px) - 28px))
      rotateX(var(--rot-x, 58deg)) rotateZ(var(--rot-z, -34deg));
  }
  to {
    opacity: 1;
    transform: translateY(var(--board-shift-y, 110px))
      translateZ(var(--camera-z, 120px)) rotateX(var(--rot-x, 58deg))
      rotateZ(var(--rot-z, -34deg));
  }
}

.layer {
  position: absolute;
  top: 0;
  left: 0;
  display: grid;
  gap: 4px;
  background: rgba(255, 255, 255, 0.72);
  border: 1px solid #dce5f3;
  border-radius: 10px;
  padding: 8px;
  transform-style: preserve-3d;
}

.layer-label {
  position: absolute;
  right: -66px;
  top: 0;
  font-size: 0.82rem;
  color: #4b5563;
  background: rgba(255, 255, 255, 0.85);
  border: 1px solid #d8dfeb;
  border-radius: 6px;
  padding: 2px 6px;
}

.cell {
  width: 38px;
  height: 38px;
  border-radius: 8px;
  border: 1px solid #ced7e5;
  background: #f5f8fc;
  display: grid;
  place-items: center;
  font-weight: 700;
  color: #627089;
}

.cell:disabled {
  cursor: not-allowed;
}

.cell.p1 {
  color: #9a3412;
  background: color-mix(in srgb, var(--p1) 24%, white);
}

.cell.p2 {
  color: #1e3a8a;
  background: color-mix(in srgb, var(--p2) 20%, white);
}

.cell.win {
  outline: 2px solid var(--win);
  outline-offset: 0;
}

.cell.drop-in {
  animation: drop-in 320ms cubic-bezier(0.2, 0.8, 0.2, 1);
  transform-style: preserve-3d;
}

@keyframes drop-in {
  from {
    transform: translate3d(
      var(--drop-from-x, 0px),
      var(--drop-from-y, 0px),
      var(--drop-from-z, 140px)
    );
    opacity: 0.55;
  }
  to {
    transform: translate3d(0, 0, 0);
    opacity: 1;
  }
}

/* ─── 4D layout ─────────────────────────────────────────────────────────── */

.board-container.mode-4d {
  /* Keep the base display:grid; place-items:center from .board-container */
  /* just adjust padding for the topbar */
  padding-top: 56px;
  padding-bottom: 24px;
  align-content: center;
}

.boards-4d {
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  gap: 52px;
  align-items: flex-start;
  justify-content: center;
  /* transform-style: flat (default) — blocks .board-container's perspective
     so each .w-section gets its own independent perspective context */
}

.w-section {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0;
  /* Own perspective context per sub-board: correct hit-testing + rendering */
  perspective: 1000px;
  perspective-origin: 50% 50%;
}

.w-section-label {
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  color: var(--accent);
  background: #def7f3;
  border: 1px solid var(--accent);
  border-radius: 6px;
  padding: 3px 10px;
  margin-top: 10px;
}

/* Smaller cells and tighter gaps inside 4D sub-boards */
.board-container.mode-4d .cell {
  width: 32px;
  height: 32px;
  font-size: 0.78rem;
  border-radius: 6px;
}

.board-container.mode-4d .layer {
  gap: 3px;
  padding: 6px;
}

.board-container.mode-4d .layer-label {
  right: -58px;
  font-size: 0.76rem;
}

/* ─────────────────────────────────────────────────────────────────────────── */

.move-log {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #f9fbfe;
  min-height: 110px;
  max-height: 220px;
  overflow: auto;
  padding: 8px;
  font-size: 0.9rem;
  color: #41506a;
  line-height: 1.5;
}

.log-row {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
}

/* ─── How to Play ────────────────────────────────────────────────────────── */

.how-to-play {
  margin-top: 14px;
  border: 1px solid var(--line);
  border-radius: 10px;
  overflow: hidden;
}

.how-to-play summary {
  cursor: pointer;
  padding: 10px 14px;
  font-size: 0.92rem;
  font-weight: 600;
  color: var(--muted);
  list-style: none;
  display: flex;
  align-items: center;
  gap: 6px;
  user-select: none;
}

.how-to-play summary::-webkit-details-marker {
  display: none;
}

.how-to-play summary::before {
  content: "▶";
  font-size: 0.7rem;
  transition: transform 160ms ease;
}

.how-to-play[open] summary::before {
  transform: rotate(90deg);
}

.how-to-play summary:hover {
  color: var(--ink);
}

.htp-body {
  padding: 4px 16px 14px;
  font-size: 0.88rem;
  line-height: 1.6;
  color: var(--ink);
}

.htp-body p {
  margin: 6px 0;
}

.htp-body h3 {
  margin: 12px 0 2px;
  font-size: 0.88rem;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.htp-body code {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  background: #f1f5fb;
  border: 1px solid var(--line);
  border-radius: 4px;
  padding: 1px 5px;
  font-size: 0.85em;
}

/* ─────────────────────────────────────────────────────────────────────────── */

@media (max-width: 980px) {
  .setup-screen {
    padding: 10px;
  }

  .game-topbar {
    top: 8px;
    left: 8px;
    right: 8px;
  }

  .app.game-fullscreen .controls {
    top: 52px;
    left: 8px;
    right: 8px;
    bottom: 8px;
    width: auto;
  }

  .app.game-fullscreen .board-container {
    padding-top: 52px;
  }
}

/* ── Simulation results ──────────────────────────────────────────────────── */
.sim-btn { margin-top: 6px; background: #444; color: #fff; }
.sim-results { margin-top: 12px; font-size: 0.82rem; }
.sim-table { border-collapse: collapse; width: 100%; }
.sim-table th,
.sim-table td { padding: 4px 8px; border: 1px solid var(--line); text-align: center; }
.sim-table th { background: #f0f4fa; font-weight: 600; }