:root {
      --bg-main: #050712;
      --bg-panel: #0f1428;
      --bg-panel-alt: #121933;
      --accent: #3af2a3;
      --accent-soft: #2bbf7c;
      --danger: #ff6b81;
      --text-main: #f5f5f5;
      --text-muted: #9ba3d6;
      --grid-line: #222b4a;
      --shadow-glow: 0 0 18px rgba(58, 242, 163, 0.35);
      --binary-colour: #7fffb0;
      --denary-colour: #7fb3ff;
      --hex-colour: #d29bff;
      --medal-bronze: #cd7f32;
      --medal-silver: #c0c0c0;
      --medal-gold: #ffd700;
      --medal-platinum: #e5e4e2;
      --medal-diamond: #7df9ff;
      --medal-legend: #ff7de5;
    }

    * { box-sizing: border-box; }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
      background: radial-gradient(circle at top, #111633 0, #050712 55%, #02030a 100%);
      color: var(--text-main);
      display: flex;
      flex-direction: column;
      align-items: center;
      margin: 0;
      padding: 20px;
      min-height: 100vh;
    }

    #header {
      display: flex;
      justify-content: center;
      align-items: center;
      width: 100%;
      margin-bottom: 14px;
    }
#titleBar {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 20px;
  width: 100%;
  max-width: 1100px;
  margin: 0 auto;
}

#titleText {
  flex: 1;
  text-align: center;
}

#titleText h1 {
  margin: 0;
  letter-spacing: 0.18em;
  font-size: 2.8rem;
  text-transform: uppercase;
  color: var(--accent);
  text-shadow: 0 0 14px rgba(58, 242, 163, 0.6);
}

#titleText #subtitle {
  margin-top: 4px;
  font-size: 1.1rem;
  color: var(--text-muted);
}


    
    

    

    

    
#logo {
      width: 120px;
      height: 120px;
      border-radius: 50%;
      object-fit: cover;
      background: radial-gradient(circle at center, #ffffff1a, #00000000);
      box-shadow: 0 0 16px rgba(0,0,0,0.6);
    }

    #titleBlock h1 {
      margin: 0 0 2px;
      letter-spacing: 0.14em;
      font-size: 1.6rem;
      text-transform: uppercase;
      color: var(--accent);
      text-shadow: 0 0 8px rgba(58, 242, 163, 0.4);
    }

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

    #shell {
      display: flex;
      flex-direction: column;
      gap: 12px;
      max-width: 1040px;
      width: 100%;
      align-items: stretch;
    }

    #topRow {
      display: flex;
      gap: 12px;
      flex-wrap: wrap;
      align-items: stretch;
    }

    #aboutPanel {
      flex: 1 1 260px;
      padding: 12px 14px;
      border-radius: 10px;
      background: linear-gradient(135deg, rgba(18, 25, 60, 0.95), rgba(9, 15, 35, 0.98));
      border: 1px solid rgba(58, 242, 163, 0.35);
      box-shadow: var(--shadow-glow);
      font-size: 0.9rem;
    }

    #aboutTitle {
      display: flex;
      align-items: center;
      gap: 6px;
      margin-bottom: 6px;
    }

    #aboutTitle span {
      font-size: 0.78rem;
      color: var(--accent-soft);
      text-transform: uppercase;
      letter-spacing: 0.14em;
    }

    #gameTag {
      display: inline-flex;
      align-items: center;
      gap: 4px;
      padding: 3px 7px;
      border-radius: 999px;
      background: rgba(3, 205, 118, 0.12);
      border: 1px solid rgba(58, 242, 163, 0.5);
      font-size: 0.7rem;
      text-transform: uppercase;
      letter-spacing: 0.12em;
    }

    #aboutPanel p { margin: 4px 0; line-height: 1.4; }

    #gameContainer {
      display: flex;
      gap: 14px;
      flex-wrap: wrap;
      justify-content: center;
      align-items: flex-start;
    }

    #canvasWrapper {
      position: relative;
      flex: 0 1 600px;
      display: flex;
      flex-direction: column;
      justify-content: flex-end;
    }

    canvas {
      background: radial-gradient(circle at top, #131834 0, #050813 55%, #02030a 100%);
      border-radius: 12px;
      border: 2px solid #263057;
      box-shadow: 0 0 22px rgba(0, 0, 0, 0.7);
      height: 545px;
      width: auto;
      max-width: 100%;
    }

    #levelBanner {
      position: absolute;
      top: 16px;
      left: 50%;
      transform: translateX(-50%) translateY(-10px);
      padding: 6px 14px;
      border-radius: 999px;
      background: rgba(58, 242, 163, 0.14);
      border: 1px solid rgba(58, 242, 163, 0.7);
      color: #f5f5f5;
      font-size: 0.86rem;
      letter-spacing: 0.16em;
      text-transform: uppercase;
      opacity: 0;
      pointer-events: none;
      transition: opacity 0.3s ease, transform 0.3s ease;
      text-shadow: 0 0 8px rgba(58, 242, 163, 0.5);
      text-align: center;
      max-width: 90%;
    }

    #levelBanner.show {
      opacity: 1;
      transform: translateX(-50%) translateY(0);
    }

    #rightColumn {
      display: flex;
      flex-direction: column;
      gap: 10px;
      flex: 0 1 300px;
    }

    #uiPanel {
      padding: 12px 14px;
      background: linear-gradient(145deg, #0c1225, #101731);
      border-radius: 12px;
      border: 1px solid #2d3a6b;
      box-shadow: 0 10px 18px rgba(0,0,0,0.7);
      font-size: 0.92rem;
    }

    #uiPanel h2 {
      margin: 0 0 6px;
      font-size: 1.02rem;
      color: var(--accent);
      display: flex;
      align-items: center;
      justify-content: space-between;
    }

    #uiPanel h2 span {
      font-size: 0.74rem;
      text-transform: uppercase;
      letter-spacing: 0.18em;
      color: var(--text-muted);
    }

    .divider {
      border-top: 1px solid rgba(61, 77, 140, 0.9);
      margin: 6px 0 8px;
    }

    .statRow {
      display: flex;
      justify-content: space-between;
      font-size: 0.86rem;
      margin: 3px 0;
    }

    .statLabel { color: var(--text-muted); }
    .statValue { font-weight: 600; }
    #modeLabel { color: var(--accent-soft); }

    #difficultySelect {
      width: 100%;
      padding: 4px 6px;
      border-radius: 6px;
      border: 1px solid #3af2a3;
      background: #050813;
      color: #f5f5f5;
      font-size: 0.82rem;
    }

    .mode-group {
      margin-top: 6px;
      border-radius: 8px;
      border: 1px solid rgba(61,77,140,0.9);
      background: rgba(7, 11, 29, 0.9);
      overflow: hidden;
    }

    .mode-group-header {
      padding: 5px 8px;
      font-size: 0.82rem;
      display: flex;
      justify-content: space-between;
      align-items: center;
      user-select: none;
    }

    .mode-group-header span {
      text-transform: uppercase;
      letter-spacing: 0.12em;
      color: var(--text-muted);
    }

    .mode-group-body {
      padding: 6px 6px 8px;
    }

    .btn-row {
      display: flex;
      flex-wrap: wrap;
      gap: 6px;
      margin-bottom: 4px;
    }

    button {
      padding: 5px 8px;
      border-radius: 6px;
      border: 1px solid #3af2a3;
      background: #0b1530;
      color: var(--text-main);
      cursor: pointer;
      font-size: 0.8rem;
      transition: background 0.12s ease, transform 0.08s ease, box-shadow 0.12s;
    }

    button.active {
      background: var(--accent);
      color: #050813;
      font-weight: 600;
      box-shadow: 0 0 10px rgba(58, 242, 163, 0.5);
    }

    button:hover { filter: brightness(1.1); transform: translateY(-1px); }
    button:active { transform: translateY(0); box-shadow: none; }

    .help-btn {
      font-size: 0.74rem;
      padding: 3px 7px;
    }
    .help-arith { border-color: #7fb3ff; }
    .help-bin   { border-color: #3af2a3; }
    .help-hex   { border-color: #d29bff; }

    .link-btn {
      font-size: 0.74rem;
      padding: 3px 7px;
      border-style: dashed;
    }

    label {
      font-size: 0.84rem;
      margin-top: 4px;
      display: block;
    }

    #answerInput {
      width: 100%;
      padding: 7px 9px;
      border-radius: 7px;
      border: 1px solid rgba(58, 242, 163, 0.7);
      background: #050813;
      color: #f5f5f5;
      font-size: 0.9rem;
      margin: 5px 0 3px;
    }

    #answerInput:focus {
      outline: 2px solid rgba(58, 242, 163, 0.9);
      outline-offset: 1px;
    }

    .hint {
      font-size: 0.75rem;
      color: var(--text-muted);
      margin-bottom: 6px;
      line-height: 1.4;
    }

    .hint code {
      background: #050813;
      padding: 1px 4px;
      border-radius: 4px;
      font-size: 0.72rem;
    }

    #message {
      min-height: 20px;
      font-size: 0.8rem;
      margin-top: 3px;
    }
    #message.good { color: var(--accent); }
    #message.bad  { color: var(--danger); }

    #footer {
      margin-top: 8px;
      font-size: 0.78rem;
      color: var(--text-muted);
      text-align: left;
      line-height: 1.35;
    }

    #footer code {
      background: #050813;
      padding: 1px 4px;
      border-radius: 4px;
    }

    #rulesRef {
      margin-top: 0;
      padding: 8px 9px;
      border-radius: 8px;
      background: rgba(5, 9, 25, 0.85);
      border: 1px solid rgba(72, 98, 189, 0.85);
      font-size: 0.78rem;
    }

    #rulesRefTitle {
      font-size: 0.78rem;
      text-transform: uppercase;
      letter-spacing: 0.16em;
      color: var(--accent-soft);
      margin-bottom: 4px;
    }

    .rulesBlock { margin-top: 4px; }
    .rulesHeading { font-weight: 600; color: var(--text-main); margin-bottom: 2px; }

    .rulesLines {
      font-family: "Consolas", "Courier New", monospace;
      line-height: 1.25;
      color: var(--text-muted);
      white-space: pre;
    }

    #highScoresPanel {
      padding: 8px 10px;
      background: linear-gradient(145deg, #0b1123, #0f1731);
      border-radius: 10px;
      border: 1px solid #2d3a6b;
      box-shadow: 0 6px 14px rgba(0,0,0,0.6);
      font-size: 0.8rem;
    }

    #highScoresTitle {
      font-size: 0.8rem;
      text-transform: uppercase;
      letter-spacing: 0.14em;
      color: var(--accent-soft);
      margin-bottom: 4px;
    }

    .hs-groupTitle {
      font-weight: 600;
      margin-top: 4px;
      color: #c7cdf8;
    }

    .hs-line {
      display: flex;
      justify-content: space-between;
      margin: 1px 0;
      color: var(--text-muted);
    }

    .hs-line span:first-child { margin-right: 8px; }

    #infoRow {
      display: flex;
      flex-wrap: wrap;
      gap: 10px;
      margin-top: 10px;
    }

    #infoRow > * {
      flex: 1 1 320px;
    }

    /* Answer panel directly under the game */
    #answerPanel {
  margin-top: 20px;
  width: 100%;
  display: flex;
  justify-content: center;
}

    #answerCard {
      max-width: 600px;
      width: 100%;
      padding: 10px 14px;
      border-radius: 10px;
      background: linear-gradient(145deg, #0c1225, #101731);
      border: 1px solid #2d3a6b;
      box-shadow: 0 8px 16px rgba(0,0,0,0.7);
      font-size: 0.9rem;
    }

    #answerCard label {
      margin-top: 0;
    }

    #answerCard #answerInput {
      width: 100%;
      margin-top: 4px;
      margin-bottom: 4px;
    }

    #answerCard .hint {
      margin-bottom: 4px;
    }

    #answerCard #message {
      min-height: 20px;
    }

    /* Overlays */
    .overlay {
      position: fixed;
      inset: 0;
      background: rgba(0,0,0,0.7);
      display: flex;
      align-items: center;
      justify-content: center;
      z-index: 999;
    }
    .overlay.hidden { display: none; }

    .overlay-card {
      max-width: 420px;
      width: 90%;
      background: #0f1428;
      border-radius: 12px;
      border: 1px solid #3af2a3;
      box-shadow: 0 0 20px rgba(0,0,0,0.8);
      padding: 14px 16px 12px;
      font-size: 0.9rem;
      color: #f5f5f5;
    }
    .overlay-card h3 {
      margin: 0 0 6px;
      font-size: 1rem;
      color: #3af2a3;
    }
    .overlay-card p {
      margin: 4px 0;
      line-height: 1.4;
      color: #c9cff7;
    }
    .overlay-card ul {
      margin: 4px 0 8px 18px;
      padding: 0;
      color: #c9cff7;
      font-size: 0.86rem;
    }
    .overlay-card li { margin-bottom: 3px; }
    .overlay-close {
      margin-top: 8px;
      display: inline-block;
      padding: 5px 10px;
      border-radius: 6px;
      border: 1px solid #3af2a3;
      background: #0b1530;
      color: #f5f5f5;
      cursor: pointer;
      font-size: 0.8rem;
    }
    .overlay-close:hover { filter: brightness(1.1); }

    #gameOverCard {
      border-color: #ffd700;
      text-align: center;
    }
    #gameOverTitle {
      font-size: 1.1rem;
      margin-bottom: 4px;
    }
    #gameOverMedal {
      font-weight: 700;
      margin: 3px 0;
    }
    .medal-bronze { color: var(--medal-bronze); }
    .medal-silver { color: var(--medal-silver); }
    .medal-gold { color: var(--medal-gold); }
    .medal-platinum { color: var(--medal-platinum); }
    .medal-diamond { color: var(--medal-diamond); }
    .medal-legend { color: var(--medal-legend); }

    @media (max-width: 780px) {
      #gameContainer {
        flex-direction: column;
        align-items: center;
      }
      #rightColumn {
        max-width: 600px;
        width: 100%;
      }
      #canvasWrapper {
        flex: 1 1 auto;
      }
    }
  
    /* Rules toggle button & floating rules panel */
    #rulesToggleBtn {
      margin-top: 6px;
      width: 100%;
    }

    body.rules-floating #infoRow > * {
      display: none;
    }

    body.rules-floating #rulesRef {
      display: block;
      position: fixed;
      right: 16px;
      top: 50%;
      transform: translateY(-50%);
      max-width: 280px;
      z-index: 500;
    }

    @media (max-width: 900px) {
      body.rules-floating #rulesRef {
        left: 50%;
        right: auto;
        transform: translate(-50%, -50%);
        width: 90%;
      }
    }

/* === Final alignment tweak: remove gap between canvas and answer box === */
#canvasWrapper {
  margin-bottom: 0 !important;
  padding-bottom: 0 !important;
}

canvas

@media (min-width: 1024px) {
  #answerPanel {
  margin-top: 20px;
  width: 100%;
  display: flex;
  justify-content: center;
}
}






/* === Unified layout: game window & Modes panel same height === */
:root {
  --panel-height: 780px;
}

#gameContainer {
  display: flex;
  gap: 14px;
  flex-wrap: nowrap;
  justify-content: center;
  align-items: stretch;
}

#canvasWrapper,
#rightColumn {
  height: var(--panel-height);
  display: flex;
  flex-direction: column;
}

#canvasWrapper {
  flex: 0 1 640px;
}

#rightColumn {
  flex: 0 1 320px;
}

#canvasWrapper canvas {
  flex: 1 1 auto;
  width: 100%;
  height: 100%;
}

#rightColumn > #uiPanel {
  flex: 1 1 auto;
  display: flex;
  flex-direction: column;
}

/* On smaller screens, revert to stacked layout */
@media (max-width: 900px) {
  #gameContainer {
    flex-wrap: wrap;
    align-items: flex-start;
  }
  #canvasWrapper,
  #rightColumn {
    height: auto;
  }
}