:root {
    --bg: #201713;
    --surface: #2a1d18;
    --surface-alt: #8f4c2c;
    --surface-soft: #3a2922;
    --text: #f3efe9;
    --muted: #d5cabe;
    --line: rgba(255, 255, 255, 0.12);
    --white-cell: #f3efe9;
    --white-lit: #f0d49a;
    --black-cell: #3a2922;
    --good: #355038;
    --bad: #6b2e2e;
    --accent: #cf7b39;
    --conflict: #ff7878;
    --shadow: 0 10px 30px rgba(0, 0, 0, 0.18);
  
    /* Main sizing */
    --board-cell-size: 35px;
    --merge-cell-size: 35px;
  
    /* Merge layout */
    --merge-gap: 3rem;
    --merge-offset: 1.5rem;
  
    /* Timings */
    --merge-move-duration: 5.0s;
    --merge-fade-duration: 3s;
    --final-image-fade-duration: 7s;
  }
  
  * {
    box-sizing: border-box;
  }
  
  html {
    scroll-behavior: smooth;
  }
  
  body {
    margin: 0;
    background: var(--bg);
    color: var(--text);
    font-family: Arial, Helvetica, sans-serif;
    line-height: 1.5;
  }
  
  button,
  input,
  select,
  textarea {
    font: inherit;
  }
  
  a {
    color: var(--text);
    text-decoration: underline;
    text-underline-offset: 0.15em;
  }
  
  .app {
    width: min(calc(100% - 2rem), 1080px);
    margin: 0 auto;
    padding: 1.25rem 0 3rem;
  }
  
  .page-header {
    margin-bottom: 1rem;
  }
  
  .back-link {
    display: inline-block;
    margin-bottom: 0.8rem;
  }
  
  .page-header h1 {
    margin: 0 0 0.6rem;
    font-size: clamp(1.9rem, 4vw, 3rem);
    line-height: 1.1;
  }
  
  .page-header p {
    margin: 0.5rem 0 0;
    color: var(--muted);
  }
  
  .rules {
    max-width: 70ch;
    color: var(--muted);
  }
  
  .rules p {
    margin: 0.8rem 0 0.35rem;
  }
  
  .rules ul {
    margin: 0.2rem 0 0.8rem 1.2rem;
    padding: 0;
  }
  
  .rules li {
    margin: 0.2rem 0;
  }
  
  .progress {
    display: flex;
    flex-wrap: wrap;
    gap: 0.6rem;
    margin: 1.2rem 0;
  }
  
  .progress-step {
    min-width: 3rem;
    padding: 0.55rem 0.85rem;
    border: 1px solid var(--line);
    background: var(--surface);
    color: var(--muted);
    text-align: center;
    cursor: pointer;
  }
  
  .progress-step:disabled {
    opacity: 0.45;
    cursor: not-allowed;
  }
  
  .progress-step.current {
    border-color: var(--accent);
    color: var(--text);
  }
  
  .progress-step.solved {
    background: var(--surface-alt);
    color: var(--text);
    border-color: transparent;
  }
  
  .toolbar {
    display: flex;
    flex-wrap: wrap;
    justify-content: flex-start;
    gap: 1rem;
    margin-bottom: 1rem;
    padding: 1rem;
    background: var(--surface);
    border: 1px solid var(--line);
    box-shadow: var(--shadow);
  }
  
  .action-group {
    display: flex;
    flex-wrap: wrap;
    gap: 0.6rem;
  }
  
  .toolbar button {
    border: 1px solid var(--line);
    background: transparent;
    color: var(--text);
    padding: 0.55rem 0.85rem;
    cursor: pointer;
  }
  
  .toolbar button:disabled {
    opacity: 0.45;
    cursor: not-allowed;
  }
  
  .game-area {
    display: grid;
  }
  
  .board-shell,
  .merge-scene {
    grid-area: 1 / 1;
    background: var(--surface);
    border: 1px solid var(--line);
    box-shadow: var(--shadow);
  }
  
  .board-shell {
    padding: 1rem;
    overflow-x: auto;
  }
  
  .board-wrap {
    position: relative;
    width: max-content;
    margin: 0 auto;
    transition: transform 0.35s ease;
  }
  
  .board-shell.final-stage .board-wrap {
    transform: translate(-2px, 27px);
  }
  
  .board {
    --cell-size: var(--board-cell-size);
    display: grid;
    grid-template-columns: repeat(var(--cols), var(--cell-size));
    gap: 2px;
    width: max-content;
    background: var(--surface-alt);
    padding: 2px;
    margin: 0;
  }
  
  .board-actions {
    margin-top: 1rem;
    display: flex;
    justify-content: flex-start;
  }
  
  #next-button,
  #start-final {
    border: 1px solid var(--surface-alt);
    background: var(--surface-alt);
    color: var(--text);
    padding: 0.7rem 1rem;
    cursor: pointer;
  }
  
  .cell {
    width: var(--cell-size);
    aspect-ratio: 1 / 1;
    border: 0;
    padding: 0;
    display: grid;
    place-items: center;
    font-weight: 700;
    cursor: pointer;
  }
  
  .cell.white {
    background: var(--white-cell);
    color: #201713;
  }
  
  .cell.white.lit {
    background: var(--white-lit);
  }
  
  .cell.black {
    background: var(--black-cell);
    color: var(--text);
    cursor: default;
    font-size: 1.75rem;
    line-height: 1;
  }
  
  .cell.white.bulb {
    color: #b5651d;
    font-size: 1.85rem;
    line-height: 1;
  }
  
  .cell.white.mark {
    color: #7f6251;
    font-size: 1.75rem;
    line-height: 1;
  }
  
  .cell.black.good {
    background: var(--good);
  }
  
  .cell.black.bad {
    background: var(--bad);
  }
  
  .cell.conflict {
    outline: 3px solid var(--conflict);
    outline-offset: -3px;
    position: relative;
    z-index: 1;
  }
  
  .board-overlay {
    position: absolute;
    inset: 0;
    opacity: 0;
    pointer-events: none;
    transition: opacity var(--final-image-fade-duration) ease;
  }
  
  .board-overlay.show {
    opacity: 1;
  }
  
  .board-overlay-image {
    width: 100%;
    height: 100%;
    display: block;
    object-fit: fill;
    image-rendering: pixelated;
  }
  
  .merge-scene {
    padding: 1rem;
    opacity: 1;
    transition: opacity var(--merge-fade-duration) ease;
  }
  
  .merge-scene.fading-to-final {
    opacity: 0;
  }
  
  .merge-stage {
    position: relative;
    width: max-content;
    margin: 0 auto;
  }
  
  .merge-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--merge-gap);
    width: max-content;
    margin: 0 auto;
  }
  
  .merge-mini {
    padding: 0.5rem;
    background: rgba(255, 255, 255, 0.03);
    border: 1px solid var(--line);
    transition: transform var(--merge-move-duration) ease, opacity 0.6s ease;
  }
  
  .merge-grid.assembling .merge-mini:nth-child(1) {
    transform: translate(var(--merge-offset), var(--merge-offset));
  }
  
  .merge-grid.assembling .merge-mini:nth-child(2) {
    transform: translate(calc(-1 * var(--merge-offset)), var(--merge-offset));
  }
  
  .merge-grid.assembling .merge-mini:nth-child(3) {
    transform: translate(var(--merge-offset), calc(-1 * var(--merge-offset)));
  }
  
  .merge-grid.assembling .merge-mini:nth-child(4) {
    transform: translate(calc(-1 * var(--merge-offset)), calc(-1 * var(--merge-offset)));
  }
  
  #start-final {
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
    z-index: 5;
  }
  
  .merge-scene.assembling #start-final {
    opacity: 0;
    pointer-events: none;
  }
  
  .mini-board {
    --mini-cell-size: var(--merge-cell-size);
    display: grid;
    grid-template-columns: repeat(var(--cols), var(--mini-cell-size));
    gap: 1px;
    width: max-content;
    margin: 0 auto;
    background: var(--surface-alt);
    padding: 1px;
  }
  
  .mini-cell {
    width: var(--mini-cell-size);
    aspect-ratio: 1 / 1;
    display: grid;
    place-items: center;
    font-weight: 700;
    line-height: 1;
  }
  
  .mini-cell.white {
    background: var(--white-cell);
    color: #201713;
  }
  
  .mini-cell.white.lit {
    background: var(--white-lit);
  }
  
  .mini-cell.black {
    background: var(--black-cell);
    color: var(--text);
  }
  
  .mini-cell.clue {
    font-size: 1.15rem;
  }
  
  .mini-cell.bulb {
    font-size: 1.8rem;
    color: #b5651d;
  }
  
  .mini-cell.mark {
    font-size: 1.65rem;
    color: #7f6251;
  }
  
  .hidden {
    display: none !important;
  }
  
  @media (max-width: 860px) {
    :root {
      --board-cell-size: 34px;
      --merge-cell-size: 34px;
      --merge-gap: 2rem;
      --merge-offset: 1rem;
    }
  
    .cell.black {
      font-size: 1.45rem;
    }
  
    .cell.white.bulb {
      font-size: 1.55rem;
    }
  
    .cell.white.mark {
      font-size: 1.45rem;
    }
  
    .mini-cell.clue {
      font-size: 0.95rem;
    }
  
    .mini-cell.bulb {
      font-size: 1.3rem;
    }
  
    .mini-cell.mark {
      font-size: 1.2rem;
    }
  }
  
  @media (max-width: 620px) {
    .app {
      width: min(calc(100% - 1rem), 1080px);
    }
  
    .toolbar {
      padding: 0.8rem;
    }
  
    .board {
      --cell-size: min(9vw, 30px);
    }
  
    .mini-board {
      --mini-cell-size: min(9vw, 30px);
    }
  
    .cell.black {
      font-size: 1.2rem;
    }
  
    .cell.white.bulb {
      font-size: 1.3rem;
    }
  
    .cell.white.mark {
      font-size: 1.2rem;
    }
  
    .mini-cell.clue {
      font-size: 0.8rem;
    }
  
    .mini-cell.bulb {
      font-size: 1.05rem;
    }
  
    .mini-cell.mark {
      font-size: 0.95rem;
    }
  }