<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      -webkit-tap-highlight-color: transparent;
    }

    body {
      width: 100%;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: transparent;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 16px 8px;
      user-select: none;
    }

    .diagram-grid {
      width: 100%;
      max-width: 580px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 14px;
    }

    /* Columns container */
    .numeral-row {
      display: grid;
      grid-template-columns: repeat(7, 1fr);
      gap: 6px;
      width: 100%;
    }

    .col-item {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 6px;
      cursor: pointer;
    }

    /* Roman Numeral Badges */
    .roman-badge {
      width: 100%;
      aspect-ratio: 1;
      max-width: 68px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: clamp(18px, 4.5vw, 28px);
      font-weight: 800;
      border-radius: 12px;
      color: #ffffff;
      transition: filter 0.2s ease, transform 0.2s ease;
      box-shadow: 0 3px 6px rgba(0, 0, 0, 0.08);
    }

    /* Arrows */
    .arrow-icon {
      font-size: clamp(14px, 3.2vw, 18px);
      font-weight: 900;
      color: #94a3b8;
      transition: color 0.2s ease;
    }

    /* Value Badges */
    .val-badge {
      width: 100%;
      padding: 6px 2px;
      border-radius: 8px;
      text-align: center;
      font-size: clamp(11px, 2.6vw, 16px);
      font-weight: 700;
      background: #f1f5f9;
      color: #334155;
      border: 1.5px solid #e2e8f0;
      transition: background 0.2s ease, border-color 0.2s ease, color 0.2s ease;
    }

    /* Color scheme - spectrum for descending values */
    .c-m { background: #6366f1; } /* 1000 */
    .c-d { background: #3b82f6; } /* 500 */
    .c-c { background: #06b6d4; } /* 100 */
    .c-l { background: #10b981; } /* 50 */
    .c-x { background: #f59e0b; } /* 10 */
    .c-v { background: #f97316; } /* 5 */
    .c-i { background: #ec4899; } /* 1 */

    /* Active / Focused Column */
    .col-item.active .roman-badge {
      filter: brightness(1.1);
      outline: 3px solid #1e2945;
      outline-offset: 2px;
    }
    .col-item.active .arrow-icon {
      color: #1e2945;
    }
    .col-item.active .val-badge {
      background: #1e2945;
      color: #ffffff;
      border-color: #1e2945;
    }

    /* Addition expression row */
    .math-row {
      display: flex;
      align-items: center;
      justify-content: center;
      flex-wrap: wrap;
      gap: 4px clamp(2px, 1vw, 6px);
      padding: 8px 12px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      font-size: clamp(12px, 2.8vw, 16px);
      font-weight: 600;
      color: #475569;
      width: 100%;
    }

    .math-term {
      padding: 2px 4px;
      border-radius: 4px;
      transition: background 0.2s ease, color 0.2s ease;
    }
    .math-term.active {
      background: #1e2945;
      color: #ffffff;
    }

    .plus-sign {
      color: #94a3b8;
      font-weight: 700;
    }

    /* Total result box */
    .total-box {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 10px;
      background: #ecfdf5;
      border: 2px solid #10b981;
      padding: 10px 24px;
      border-radius: 12px;
      color: #065f46;
      font-size: clamp(18px, 4.5vw, 24px);
      font-weight: 800;
      box-shadow: 0 4px 10px rgba(16, 185, 129, 0.12);
    }

    .total-label {
      font-size: clamp(14px, 3.2vw, 16px);
      font-weight: 700;
      color: #047857;
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }
  </style>
</head>
<body>
  <div class="diagram-grid">
    
    <div class="numeral-row">
      <div class="col-item" data-idx="0">
        <div class="roman-badge c-m">M</div>
        <div class="arrow-icon">↓</div>
        <div class="val-badge">1000</div>
      </div>
      <div class="col-item" data-idx="1">
        <div class="roman-badge c-d">D</div>
        <div class="arrow-icon">↓</div>
        <div class="val-badge">500</div>
      </div>
      <div class="col-item" data-idx="2">
        <div class="roman-badge c-c">C</div>
        <div class="arrow-icon">↓</div>
        <div class="val-badge">100</div>
      </div>
      <div class="col-item" data-idx="3">
        <div class="roman-badge c-l">L</div>
        <div class="arrow-icon">↓</div>
        <div class="val-badge">50</div>
      </div>
      <div class="col-item" data-idx="4">
        <div class="roman-badge c-x">X</div>
        <div class="arrow-icon">↓</div>
        <div class="val-badge">10</div>
      </div>
      <div class="col-item" data-idx="5">
        <div class="roman-badge c-v">V</div>
        <div class="arrow-icon">↓</div>
        <div class="val-badge">5</div>
      </div>
      <div class="col-item" data-idx="6">
        <div class="roman-badge c-i">I</div>
        <div class="arrow-icon">↓</div>
        <div class="val-badge">1</div>
      </div>
    </div>

    
    <div class="math-row">
      <span class="math-term" data-idx="0">1000</span>
      <span class="plus-sign">+</span>
      <span class="math-term" data-idx="1">500</span>
      <span class="plus-sign">+</span>
      <span class="math-term" data-idx="2">100</span>
      <span class="plus-sign">+</span>
      <span class="math-term" data-idx="3">50</span>
      <span class="plus-sign">+</span>
      <span class="math-term" data-idx="4">10</span>
      <span class="plus-sign">+</span>
      <span class="math-term" data-idx="5">5</span>
      <span class="plus-sign">+</span>
      <span class="math-term" data-idx="6">1</span>
    </div>

    
    <div class="total-box">
      <span class="total-label">Total</span>
      <span>= 1,666</span>
    </div>
  </div>

  <script>
    const cols = document.querySelectorAll('.col-item');
    const terms = document.querySelectorAll('.math-term');

    function setActive(idx) {
      cols.forEach((col, i) => {
        if (i === idx) {
          col.classList.toggle('active');
        } else {
          col.classList.remove('active');
        }
      });

      terms.forEach((term, i) => {
        const isActive = cols[i].classList.contains('active');
        term.classList.toggle('active', isActive);
      });
    }

    cols.forEach((col, idx) => {
      col.addEventListener('click', () => setActive(idx));
    });

    terms.forEach((term, idx) => {
      term.addEventListener('click', () => setActive(idx));
    });
  </script>
</body>
</html>

Roman Numeral Symbols and Adding Rules

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      -webkit-tap-highlight-color: transparent;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #f8fafc;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      padding: 12px;
      gap: 10px;
    }

    .columns {
      display: grid;
      grid-template-columns: 1.2fr 1fr;
      gap: 12px;
      width: 100%;
    }

    @media (max-width: 520px) {
      .columns {
        grid-template-columns: 1fr;
      }
    }

    .column {
      background: #ffffff;
      border-radius: 12px;
      padding: 12px;
      display: flex;
      flex-direction: column;
      gap: 8px;
      box-shadow: 0 1px 3px rgba(0, 0, 0, 0.05);
      border: 1px solid #e2e8f0;
    }

    .col-header {
      display: flex;
      align-items: center;
      gap: 8px;
      padding-bottom: 8px;
      border-bottom: 2px solid #f1f5f9;
      font-weight: 700;
      font-size: 15px;
    }

    .icon-badge {
      width: 24px;
      height: 24px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 13px;
      font-weight: 900;
      flex-shrink: 0;
    }

    .col-repeat .icon-badge {
      background: #dcfce7;
      color: #16a34a;
    }

    .col-repeat .col-header {
      color: #15803d;
    }

    .col-never .icon-badge {
      background: #fee2e2;
      color: #dc2626;
    }

    .col-never .col-header {
      color: #b91c1c;
    }

    .item-group {
      display: flex;
      flex-direction: column;
      gap: 6px;
    }

    .card-row {
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 6px 10px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      transition: background-color 0.2s ease, border-color 0.2s ease;
      cursor: pointer;
    }

    .card-row:hover, .card-row.active {
      background: #f1f5f9;
      border-color: #cbd5e1;
    }

    .pills {
      display: flex;
      align-items: center;
      gap: 6px;
      flex-wrap: wrap;
    }

    .num-pill {
      font-family: ui-monospace, "Cascadia Code", "Source Code Pro", Menlo, monospace;
      font-weight: 700;
      font-size: 14px;
      letter-spacing: 0.5px;
      background: #ffffff;
      padding: 3px 8px;
      border-radius: 6px;
      border: 1px solid #e2e8f0;
      color: #0f172a;
    }

    .sub-value {
      font-size: 12px;
      font-weight: 600;
      color: #64748b;
    }

    /* Forbidden column styles */
    .cross-pill {
      font-family: ui-monospace, "Cascadia Code", "Source Code Pro", Menlo, monospace;
      font-weight: 700;
      font-size: 14px;
      background: #fee2e2;
      color: #991b1b;
      padding: 3px 8px;
      border-radius: 6px;
      border: 1px solid #fecaca;
      text-decoration: line-through;
      text-decoration-thickness: 2px;
    }

    .replace-arrow {
      color: #64748b;
      font-weight: 700;
      font-size: 14px;
    }

    .valid-pill {
      font-family: ui-monospace, "Cascadia Code", "Source Code Pro", Menlo, monospace;
      font-weight: 700;
      font-size: 14px;
      background: #dcfce7;
      color: #166534;
      padding: 3px 8px;
      border-radius: 6px;
      border: 1px solid #bbf7d0;
    }

    /* Interactive Info Bar */
    .info-bar {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 8px 14px;
      font-size: 13px;
      font-weight: 600;
      color: #334155;
      text-align: center;
      min-height: 38px;
      display: flex;
      align-items: center;
      justify-content: center;
      box-shadow: 0 1px 2px rgba(0, 0, 0, 0.04);
    }

    .math-eq {
      font-family: ui-monospace, "Cascadia Code", Menlo, monospace;
      color: #0284c7;
      font-weight: 700;
    }
  </style>
</head>
<body>

  <div class="columns">
    
    <div class="column col-repeat">
      <div class="col-header">
        <span class="icon-badge">✓</span>
        <span>Repeatable (Max 3)</span>
      </div>
      <div class="item-group">
        <div class="card-row" onclick="showInfo('I = 1 &nbsp;•&nbsp; II = 2 &nbsp;•&nbsp; III = 3')">
          <div class="pills">
            <span class="num-pill">I</span>
            <span class="num-pill">II</span>
            <span class="num-pill">III</span>
          </div>
          <span class="sub-value">1, 2, 3</span>
        </div>

        <div class="card-row" onclick="showInfo('X = 10 &nbsp;•&nbsp; XX = 20 &nbsp;•&nbsp; XXX = 30')">
          <div class="pills">
            <span class="num-pill">X</span>
            <span class="num-pill">XX</span>
            <span class="num-pill">XXX</span>
          </div>
          <span class="sub-value">10, 20, 30</span>
        </div>

        <div class="card-row" onclick="showInfo('C = 100 &nbsp;•&nbsp; CC = 200 &nbsp;•&nbsp; CCC = 300')">
          <div class="pills">
            <span class="num-pill">C</span>
            <span class="num-pill">CC</span>
            <span class="num-pill">CCC</span>
          </div>
          <span class="sub-value">100, 200, 300</span>
        </div>

        <div class="card-row" onclick="showInfo('M = 1000 &nbsp;•&nbsp; MM = 2000 &nbsp;•&nbsp; MMM = 3000')">
          <div class="pills">
            <span class="num-pill">M</span>
            <span class="num-pill">MM</span>
            <span class="num-pill">MMM</span>
          </div>
          <span class="sub-value">1k, 2k, 3k</span>
        </div>
      </div>
    </div>

    
    <div class="column col-never">
      <div class="col-header">
        <span class="icon-badge">✕</span>
        <span>Never Repeat</span>
      </div>
      <div class="item-group">
        <div class="card-row" onclick="showInfo('5 + 5 = 10 &nbsp;➔&nbsp; Use X instead of VV')">
          <div class="pills">
            <span class="cross-pill">VV</span>
            <span class="replace-arrow">→</span>
            <span class="valid-pill">X</span>
          </div>
          <span class="sub-value">10</span>
        </div>

        <div class="card-row" onclick="showInfo('50 + 50 = 100 &nbsp;➔&nbsp; Use C instead of LL')">
          <div class="pills">
            <span class="cross-pill">LL</span>
            <span class="replace-arrow">→</span>
            <span class="valid-pill">C</span>
          </div>
          <span class="sub-value">100</span>
        </div>

        <div class="card-row" onclick="showInfo('500 + 500 = 1000 &nbsp;➔&nbsp; Use M instead of DD')">
          <div class="pills">
            <span class="cross-pill">DD</span>
            <span class="replace-arrow">→</span>
            <span class="valid-pill">M</span>
          </div>
          <span class="sub-value">1000</span>
        </div>
      </div>
    </div>
  </div>

  <div id="infoText" class="info-bar">
    Tap any row to inspect values
  </div>

  <script>
    function showInfo(msg) {
      document.getElementById('infoText').innerHTML = msg;
    }
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Roman Numeral Addition: MMCCCXXVII</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
      color: #1e2945;
      background: transparent;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 12px 8px;
      min-height: 100vh;
      overflow-x: hidden;
    }

    .diagram {
      width: 100%;
      max-width: 540px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 10px;
    }

    /* Top Original Numeral */
    .numeral-header {
      display: flex;
      justify-content: center;
      align-items: center;
      gap: 2px;
      letter-spacing: 0.12em;
      font-size: clamp(20px, 5.5vw, 28px);
      font-weight: 800;
      font-family: Georgia, 'Times New Roman', serif;
      padding: 6px 16px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      transition: box-shadow 0.3s ease;
    }

    .c-m { color: #6366f1; }
    .c-c { color: #0284c7; }
    .c-x { color: #0d9488; }
    .c-v { color: #d97706; }
    .c-i { color: #e11d48; }

    /* Step 1: Blocks */
    .blocks-row {
      display: flex;
      flex-wrap: nowrap;
      justify-content: space-between;
      align-items: center;
      gap: clamp(2px, 1vw, 8px);
      width: 100%;
    }

    .num-block {
      flex: 1 1 0;
      min-width: 0;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: clamp(6px, 1.8vw, 10px) clamp(2px, 1vw, 10px);
      border-radius: 8px;
      border: 1px solid transparent;
      transition: transform 0.3s ease, box-shadow 0.3s ease, opacity 0.3s ease;
    }

    .b-m { background: #eef2ff; border-color: #c7d2fe; }
    .b-c { background: #f0f9ff; border-color: #bae6fd; }
    .b-x { background: #f0fdfa; border-color: #99f6e4; }
    .b-v { background: #fffbeb; border-color: #fde68a; }
    .b-i { background: #fff1f2; border-color: #fecdd3; }

    .block-roman {
      font-family: Georgia, 'Times New Roman', serif;
      font-size: clamp(12px, 3.2vw, 17px);
      font-weight: 700;
      line-height: 1.2;
      white-space: nowrap;
    }

    .block-eq {
      font-size: clamp(9px, 2vw, 11px);
      font-weight: 600;
      color: #64748b;
      margin: 1px 0;
    }

    .block-val {
      font-size: clamp(11px, 3vw, 16px);
      font-weight: 800;
      line-height: 1.2;
      white-space: nowrap;
    }

    .plus-sign {
      font-size: clamp(12px, 3vw, 18px);
      font-weight: 700;
      color: #94a3b8;
      user-select: none;
      flex-shrink: 0;
    }

    /* Step 2: Expanded Sum */
    .equation-row {
      display: flex;
      flex-wrap: nowrap;
      justify-content: center;
      align-items: center;
      gap: clamp(4px, 1.5vw, 8px);
      padding: 8px 14px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      font-size: clamp(13px, 3.5vw, 17px);
      font-weight: 700;
      font-family: system-ui, sans-serif;
      width: 100%;
    }

    /* Down arrow */
    .arrow-down {
      color: #94a3b8;
      font-size: 15px;
      line-height: 1;
      font-weight: bold;
    }

    /* Bottom Result Badge */
    .result-badge {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      background: #1e2945;
      color: #ffffff;
      padding: 8px 22px;
      border-radius: 20px;
      box-shadow: 0 4px 12px rgba(30, 41, 69, 0.15);
      font-size: clamp(18px, 4.5vw, 22px);
      font-weight: 800;
      letter-spacing: 0.03em;
    }

    .result-badge span {
      color: #38bdf8;
    }

    /* Controls */
    .stepper-nav {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 12px;
      margin-top: 4px;
    }

    .step-btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #334155;
      padding: 5px 12px;
      font-size: 12px;
      font-weight: 600;
      border-radius: 6px;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 4px;
      transition: background-color 0.2s ease, border-color 0.2s ease;
    }

    .step-btn:hover {
      background: #e2e8f0;
      border-color: #94a3b8;
    }

    .dots-container {
      display: flex;
      gap: 8px;
    }

    .dot {
      width: 10px;
      height: 10px;
      border-radius: 50%;
      background: #cbd5e1;
      cursor: pointer;
      transition: background 0.2s ease;
    }

    .dot:hover {
      background: #94a3b8;
    }

    .dot.active {
      background: #0284c7;
    }

    /* Active Highlight States */
    .step-view {
      transition: opacity 0.3s ease;
    }

    .dimmed {
      opacity: 0.3;
    }

    .highlighted {
      box-shadow: 0 0 0 2px #0284c7;
    }
  </style>
</head>
<body>
  <div class="diagram">
    
    <div class="numeral-header" id="romanFull">
      <span class="c-m">MM</span><span class="c-c">CCC</span><span class="c-x">XX</span><span class="c-v">V</span><span class="c-i">II</span>
    </div>

    <div class="arrow-down">↓</div>

    
    <div class="blocks-row step-view" id="step1">
      <div class="num-block b-m" id="b-m">
        <span class="block-roman c-m">MM</span>
        <span class="block-eq">=</span>
        <span class="block-val c-m">2000</span>
      </div>
      <span class="plus-sign">+</span>
      <div class="num-block b-c" id="b-c">
        <span class="block-roman c-c">CCC</span>
        <span class="block-eq">=</span>
        <span class="block-val c-c">300</span>
      </div>
      <span class="plus-sign">+</span>
      <div class="num-block b-x" id="b-x">
        <span class="block-roman c-x">XX</span>
        <span class="block-eq">=</span>
        <span class="block-val c-x">20</span>
      </div>
      <span class="plus-sign">+</span>
      <div class="num-block b-v" id="b-v">
        <span class="block-roman c-v">V</span>
        <span class="block-eq">=</span>
        <span class="block-val c-v">5</span>
      </div>
      <span class="plus-sign">+</span>
      <div class="num-block b-i" id="b-i">
        <span class="block-roman c-i">II</span>
        <span class="block-eq">=</span>
        <span class="block-val c-i">2</span>
      </div>
    </div>

    <div class="arrow-down">↓</div>

    
    <div class="equation-row step-view" id="step2">
      <span class="c-m">2000</span>
      <span class="plus-sign">+</span>
      <span class="c-c">300</span>
      <span class="plus-sign">+</span>
      <span class="c-x">20</span>
      <span class="plus-sign">+</span>
      <span class="c-v">5</span>
      <span class="plus-sign">+</span>
      <span class="c-i">2</span>
    </div>

    <div class="arrow-down">↓</div>

    
    <div class="result-badge step-view" id="step3">
      <span>=</span> 2,327
    </div>

    
    <div class="stepper-nav">
      <button class="step-btn" id="playBtn" type="button">⏸ Pause</button>
      <div class="dots-container">
        <div class="dot active" data-step="0" title="Full numeral"></div>
        <div class="dot" data-step="1" title="Decompose"></div>
        <div class="dot" data-step="2" title="Add values"></div>
        <div class="dot" data-step="3" title="Total sum"></div>
      </div>
    </div>
  </div>

  <script>
    const elRomanFull = document.getElementById('romanFull');
    const elStep1 = document.getElementById('step1');
    const elStep2 = document.getElementById('step2');
    const elStep3 = document.getElementById('step3');
    const dots = document.querySelectorAll('.dot');
    const playBtn = document.getElementById('playBtn');
    const numBlocks = document.querySelectorAll('.num-block');

    let currentStep = 0;
    let isPlaying = true;
    let timer = null;

    function renderStep(idx) {
      currentStep = idx;

      // Update dots
      dots.forEach((d, i) => {
        if (i === idx) d.classList.add('active');
        else d.classList.remove('active');
      });

      // Update view opacity/highlights according to active step
      if (idx === 0) {
        elRomanFull.style.boxShadow = '0 0 0 2px #0284c7';
        elStep1.classList.remove('dimmed');
        elStep2.classList.remove('dimmed');
        elStep3.classList.remove('dimmed');
        numBlocks.forEach(b => b.classList.remove('highlighted'));
      } else if (idx === 1) {
        elRomanFull.style.boxShadow = 'none';
        elStep1.classList.remove('dimmed');
        elStep2.classList.add('dimmed');
        elStep3.classList.add('dimmed');
        numBlocks.forEach(b => b.classList.add('highlighted'));
      } else if (idx === 2) {
        elRomanFull.style.boxShadow = 'none';
        elStep1.classList.add('dimmed');
        elStep2.classList.remove('dimmed');
        elStep3.classList.add('dimmed');
        numBlocks.forEach(b => b.classList.remove('highlighted'));
      } else if (idx === 3) {
        elRomanFull.style.boxShadow = 'none';
        elStep1.classList.add('dimmed');
        elStep2.classList.add('dimmed');
        elStep3.classList.remove('dimmed');
        numBlocks.forEach(b => b.classList.remove('highlighted'));
      }
    }

    function nextStep() {
      const next = (currentStep + 1) % 4;
      renderStep(next);
    }

    function startAutoPlay() {
      if (timer) clearInterval(timer);
      timer = setInterval(nextStep, 3000);
      isPlaying = true;
      playBtn.textContent = '⏸ Pause';
    }

    function stopAutoPlay() {
      if (timer) clearInterval(timer);
      timer = null;
      isPlaying = false;
      playBtn.textContent = '▶ Play';
    }

    dots.forEach((dot, index) => {
      dot.addEventListener('click', () => {
        stopAutoPlay();
        renderStep(index);
      });
    });

    playBtn.addEventListener('click', () => {
      if (isPlaying) {
        stopAutoPlay();
      } else {
        nextStep();
        startAutoPlay();
      }
    });

    // Start playback
    renderStep(0);
    startAutoPlay();
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #f8fafc;
      color: #1e2945;
      padding: 14px;
      display: flex;
      flex-direction: column;
      justify-content: center;
      min-height: 100%;
      user-select: none;
    }

    .grid-container {
      display: grid;
      grid-template-columns: repeat(7, 1fr);
      gap: 8px;
      width: 100%;
    }

    @media (max-width: 580px) {
      .grid-container {
        grid-template-columns: repeat(4, 1fr);
      }
      .card-m {
        grid-column: span 2;
      }
    }

    @media (max-width: 380px) {
      .grid-container {
        grid-template-columns: repeat(2, 1fr);
      }
      .card-m {
        grid-column: span 2;
      }
    }

    .num-card {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 12px 4px 10px 4px;
      display: flex;
      flex-direction: column;
      align-items: center;
      text-align: center;
      cursor: pointer;
      transition: border-color 0.2s ease, box-shadow 0.2s ease, background-color 0.2s ease;
      position: relative;
    }

    .num-card.active {
      border-color: #2563eb;
      background: #eff6ff;
      box-shadow: 0 4px 12px rgba(37, 99, 235, 0.12);
    }

    .roman {
      font-family: "Times New Roman", Georgia, serif;
      font-size: 32px;
      font-weight: 700;
      line-height: 1.1;
      color: #1e2945;
      margin-bottom: 2px;
    }

    .arabic {
      font-size: 16px;
      font-weight: 700;
      color: #2563eb;
      margin-bottom: 8px;
    }

    .memory-tag {
      font-size: 11px;
      font-weight: 500;
      color: #475569;
      background: #f1f5f9;
      padding: 3px 6px;
      border-radius: 6px;
      line-height: 1.2;
      white-space: nowrap;
    }

    .num-card.active .memory-tag {
      background: #dbeafe;
      color: #1d4ed8;
      font-weight: 600;
    }

    .detail-panel {
      margin-top: 14px;
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 10px 14px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      gap: 12px;
    }

    .detail-left {
      display: flex;
      align-items: baseline;
      gap: 8px;
    }

    .detail-roman {
      font-family: "Times New Roman", Georgia, serif;
      font-size: 24px;
      font-weight: 700;
      color: #1e2945;
    }

    .detail-eq {
      color: #64748b;
      font-weight: 600;
    }

    .detail-val {
      font-size: 20px;
      font-weight: 700;
      color: #2563eb;
    }

    .detail-origin {
      font-size: 13px;
      color: #475569;
      font-weight: 500;
    }

    .scale-bar {
      display: flex;
      align-items: center;
      gap: 3px;
      height: 6px;
      margin-top: 10px;
      background: #e2e8f0;
      border-radius: 3px;
      overflow: hidden;
    }

    .scale-segment {
      height: 100%;
      flex: 1;
      background: #cbd5e1;
      transition: background-color 0.2s ease;
    }

    .scale-segment.highlight {
      background: #2563eb;
    }
  </style>
</head>
<body>

  <div class="grid-container" id="cardsGrid">
    <div class="num-card active" data-idx="0" data-roman="I" data-val="1" data-desc="1 single finger stroke">
      <div class="roman">I</div>
      <div class="arabic">1</div>
      <div class="memory-tag">1 stroke</div>
    </div>

    <div class="num-card" data-idx="1" data-roman="V" data-val="5" data-desc="Hand shape (V between thumb & fingers)">
      <div class="roman">V</div>
      <div class="arabic">5</div>
      <div class="memory-tag">hand V</div>
    </div>

    <div class="num-card" data-idx="2" data-roman="X" data-val="10" data-desc="Two crossed V's (5 + 5)">
      <div class="roman">X</div>
      <div class="arabic">10</div>
      <div class="memory-tag">double V</div>
    </div>

    <div class="num-card" data-idx="3" data-roman="L" data-val="50" data-desc="Half of 100 (bottom half of early C/100)">
      <div class="roman">L</div>
      <div class="arabic">50</div>
      <div class="memory-tag">half 100</div>
    </div>

    <div class="num-card" data-idx="4" data-roman="C" data-val="100" data-desc="Centum (Latin for 100 → century)">
      <div class="roman">C</div>
      <div class="arabic">100</div>
      <div class="memory-tag">centum</div>
    </div>

    <div class="num-card" data-idx="5" data-roman="D" data-val="500" data-desc="Half of 1,000 (half of early circled M)">
      <div class="roman">D</div>
      <div class="arabic">500</div>
      <div class="memory-tag">half 1000</div>
    </div>

    <div class="num-card card-m" data-idx="6" data-roman="M" data-val="1,000" data-desc="Mille (Latin for 1,000 → millennium)">
      <div class="roman">M</div>
      <div class="arabic">1,000</div>
      <div class="memory-tag">mille</div>
    </div>
  </div>

  <div class="scale-bar" id="scaleBar">
    <div class="scale-segment highlight"></div>
    <div class="scale-segment"></div>
    <div class="scale-segment"></div>
    <div class="scale-segment"></div>
    <div class="scale-segment"></div>
    <div class="scale-segment"></div>
    <div class="scale-segment"></div>
  </div>

  <div class="detail-panel">
    <div class="detail-left">
      <span class="detail-roman" id="detailRoman">I</span>
      <span class="detail-eq">=</span>
      <span class="detail-val" id="detailVal">1</span>
    </div>
    <div class="detail-origin" id="detailDesc">1 single finger stroke</div>
  </div>

  <script>
    const cards = document.querySelectorAll('.num-card');
    const segments = document.querySelectorAll('.scale-segment');
    const detailRoman = document.getElementById('detailRoman');
    const detailVal = document.getElementById('detailVal');
    const detailDesc = document.getElementById('detailDesc');

    function selectCard(card) {
      cards.forEach(c => c.classList.remove('active'));
      card.classList.add('active');

      const idx = parseInt(card.getAttribute('data-idx'), 10);
      detailRoman.textContent = card.getAttribute('data-roman');
      detailVal.textContent = card.getAttribute('data-val');
      detailDesc.textContent = card.getAttribute('data-desc');

      segments.forEach((seg, sIdx) => {
        if (sIdx <= idx) {
          seg.classList.add('highlight');
        } else {
          seg.classList.remove('highlight');
        }
      });
    }

    cards.forEach(card => {
      card.addEventListener('click', () => selectCard(card));
    });
  </script>
</body>
</html>

OGM.6.NBT.9

Aligned learning resources

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