<!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;
      color: #1e2945;
      background: transparent;
      padding: 8px;
      display: flex;
      justify-content: center;
      align-items: center;
      min-height: 100%;
    }

    .math-var {
      font-family: "Cambria Math", "Times New Roman", Georgia, serif;
      font-style: italic;
      font-weight: 600;
    }

    .grid-container {
      display: grid;
      grid-template-columns: 1fr auto 1fr;
      gap: 12px;
      width: 100%;
      max-width: 640px;
      align-items: stretch;
    }

    .divider {
      width: 1px;
      border-left: 2px dashed #cbd5e1;
      height: 100%;
    }

    .col {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 10px;
      padding: 4px;
    }

    .pill-left {
      background: #dbeafe;
      color: #1e40af;
      font-size: 13px;
      font-weight: 700;
      padding: 5px 12px;
      border-radius: 999px;
      text-align: center;
    }

    .pill-right {
      background: #f3e8ff;
      color: #6b21a8;
      font-size: 13px;
      font-weight: 700;
      padding: 5px 12px;
      border-radius: 999px;
      text-align: center;
    }

    /* Left Column: Mystery Chest */
    .chest-stage {
      width: 100%;
      height: 110px;
      display: flex;
      align-items: center;
      justify-content: center;
      position: relative;
    }

    .chest-card {
      width: 130px;
      height: 100px;
      background: linear-gradient(180deg, #d97706 0%, #b45309 60%, #78350f 100%);
      border: 3px solid #78350f;
      border-radius: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      position: relative;
      box-shadow: inset 0 2px 4px rgba(255,255,255,0.3), 0 4px 10px rgba(0,0,0,0.12);
      transition: background 0.3s ease, border-color 0.3s ease;
    }

    .chest-card::before {
      content: '';
      position: absolute;
      top: 36px;
      left: 0;
      right: 0;
      height: 3px;
      background: #451a03;
    }

    .chest-badge {
      background: #fef3c7;
      border: 2px solid #b45309;
      border-radius: 8px;
      padding: 4px 10px;
      font-size: 18px;
      font-weight: bold;
      color: #78350f;
      display: flex;
      align-items: center;
      gap: 5px;
      z-index: 2;
      box-shadow: 0 2px 4px rgba(0,0,0,0.15);
    }

    .chest-revealed {
      background: linear-gradient(180deg, #eff6ff 0%, #dbeafe 100%);
      border-color: #2563eb;
    }

    .chest-revealed::before {
      display: none;
    }

    .chest-revealed .chest-badge {
      background: #ffffff;
      border-color: #2563eb;
      color: #1e40af;
      font-size: 19px;
    }

    .toggle-btn {
      appearance: none;
      border: 1px solid #93c5fd;
      background: #eff6ff;
      color: #1e40af;
      font-size: 13px;
      font-weight: 600;
      padding: 6px 14px;
      border-radius: 6px;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 6px;
      user-select: none;
      transition: background-color 0.2s, box-shadow 0.2s;
    }

    .toggle-btn:active {
      background: #dbeafe;
    }

    /* Right Column: Dynamic Table & Stepper */
    .data-table {
      width: 100%;
      border-collapse: collapse;
      font-size: 12px;
      border-radius: 6px;
      overflow: hidden;
      border: 1px solid #e2e8f0;
    }

    .data-table tr {
      background: #f8fafc;
      border-bottom: 1px solid #e2e8f0;
    }

    .data-table tr:last-child {
      border-bottom: none;
      background: #f1f5f9;
      font-weight: 600;
    }

    .data-table td {
      padding: 4px 8px;
      text-align: center;
    }

    .data-table td:first-child {
      text-align: left;
      border-right: 1px solid #e2e8f0;
    }

    .stepper-container {
      width: 100%;
      display: flex;
      align-items: center;
      justify-content: space-between;
      gap: 6px;
      background: #faf5ff;
      border: 1px solid #e9d5ff;
      border-radius: 8px;
      padding: 5px 8px;
    }

    .step-btn {
      appearance: none;
      border: 1px solid #c084fc;
      background: #ffffff;
      color: #6b21a8;
      font-size: 14px;
      font-weight: bold;
      width: 26px;
      height: 26px;
      border-radius: 50%;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      line-height: 1;
      user-select: none;
    }

    .step-btn:active {
      background: #f3e8ff;
    }

    .stepper-label {
      font-size: 13px;
      font-weight: 600;
      color: #581c87;
    }

    .result-callout {
      width: 100%;
      background: #f3e8ff;
      border-left: 3px solid #7c3aed;
      border-radius: 4px;
      padding: 6px 8px;
      font-size: 13px;
      font-weight: 600;
      color: #581c87;
      text-align: center;
    }

    .caption {
      font-size: 12px;
      color: #64748b;
      text-align: center;
      line-height: 1.3;
    }

    @media (max-width: 480px) {
      .grid-container {
        grid-template-columns: 1fr;
        gap: 16px;
      }
      .divider {
        width: 100%;
        height: 1px;
        border-left: none;
        border-top: 2px dashed #cbd5e1;
      }
    }
  </style>
</head>
<body>

  <div class="grid-container">
    
    
    <div class="col">
      <div class="pill-left">Fixed Unknown (1 Value)</div>

      <div class="chest-stage">
        <div id="chest" class="chest-card">
          <div id="chestBadge" class="chest-badge">
            <span>🔒</span> <span class="math-var">s</span>
          </div>
        </div>
      </div>

      <button id="toggleChestBtn" class="toggle-btn" type="button">
        <span>👁️</span> <span id="btnLabel">Reveal Value</span>
      </button>

      <div class="caption">
        1 mystery value waiting to be solved.
      </div>
    </div>

    
    <div class="divider"></div>

    
    <div class="col">
      <div class="pill-right">Changing Quantity (Many)</div>

      <table class="data-table">
        <tr>
          <td>1 lawn</td>
          <td>$8</td>
        </tr>
        <tr>
          <td>2 lawns</td>
          <td>$16</td>
        </tr>
        <tr>
          <td><span class="math-var">n</span> lawns</td>
          <td>$8 · <span class="math-var">n</span></td>
        </tr>
      </table>

      <div class="stepper-container">
        <span class="stepper-label">Lawns (<span class="math-var">n</span>):</span>
        <div style="display:flex; align-items:center; gap:8px;">
          <button id="decBtn" class="step-btn" type="button" aria-label="Decrease lawns">−</button>
          <span id="nValDisplay" style="font-size:15px; font-weight:700; min-width:14px; text-align:center;">3</span>
          <button id="incBtn" class="step-btn" type="button" aria-label="Increase lawns">+</button>
        </div>
      </div>

      <div id="resultBox" class="result-callout">
        If <span class="math-var">n</span> = 3 → <b>$24</b>
      </div>

      <div class="caption">
        <span class="math-var">n</span> varies depending on the case.
      </div>
    </div>

  </div>

  <script>
    // Left Column Interaction
    let revealed = false;
    const chest = document.getElementById('chest');
    const chestBadge = document.getElementById('chestBadge');
    const toggleChestBtn = document.getElementById('toggleChestBtn');
    const btnLabel = document.getElementById('btnLabel');

    toggleChestBtn.addEventListener('click', () => {
      revealed = !revealed;
      if (revealed) {
        chest.classList.add('chest-revealed');
        chestBadge.innerHTML = '🪙 <span class="math-var">s</span> = 14';
        btnLabel.textContent = 'Hide Value';
      } else {
        chest.classList.remove('chest-revealed');
        chestBadge.innerHTML = '🔒 <span class="math-var">s</span>';
        btnLabel.textContent = 'Reveal Value';
      }
    });

    // Right Column Interaction
    let n = 3;
    const minN = 1;
    const maxN = 6;
    const rate = 8;
    const nValDisplay = document.getElementById('nValDisplay');
    const resultBox = document.getElementById('resultBox');
    const decBtn = document.getElementById('decBtn');
    const incBtn = document.getElementById('incBtn');

    function updateChangingVar() {
      nValDisplay.textContent = n;
      resultBox.innerHTML = `If <span class="math-var">n</span> = ${n} → <b>$${n * rate}</b>`;
    }

    decBtn.addEventListener('click', () => {
      if (n > minN) {
        n--;
        updateChangingVar();
      }
    });

    incBtn.addEventListener('click', () => {
      if (n < maxN) {
        n++;
        updateChangingVar();
      }
    });
  </script>
</body>
</html>

Using Variables to Represent Unknown Numbers

<!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;
      color: #1e2945;
      background: transparent;
      padding: 10px;
      display: flex;
      flex-direction: column;
      gap: 10px;
      min-height: 100%;
    }

    .comparison {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
      align-items: stretch;
    }

    @media (max-width: 480px) {
      .comparison {
        grid-template-columns: 1fr;
        gap: 14px;
      }
    }

    .col {
      display: flex;
      flex-direction: column;
      align-items: center;
      padding: 12px 10px;
      border-radius: 12px;
      position: relative;
    }

    .col-wrong {
      background: #fef2f2;
      border: 1.5px dashed #f87171;
    }

    .col-right {
      background: #f0fdf4;
      border: 1.5px solid #86efac;
    }

    /* Badges */
    .badge {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      font-size: 13px;
      font-weight: 700;
      padding: 4px 12px;
      border-radius: 20px;
      margin-bottom: 12px;
      letter-spacing: 0.2px;
    }

    .badge-wrong {
      background: #dc2626;
      color: #ffffff;
    }

    .badge-right {
      background: #16a34a;
      color: #ffffff;
    }

    /* Variable styling */
    .var {
      font-family: "Times New Roman", Times, Georgia, serif;
      font-style: italic;
      font-weight: 700;
    }

    /* Wrong Column Elements */
    .prohibition-box {
      position: relative;
      width: 90px;
      height: 90px;
      display: flex;
      align-items: center;
      justify-content: center;
      margin: 4px 0 10px 0;
    }

    .prohibition-svg {
      position: absolute;
      inset: 0;
      width: 100%;
      height: 100%;
      pointer-events: none;
    }

    .equation-box {
      font-size: 18px;
      font-weight: 600;
      padding: 6px 14px;
      border-radius: 8px;
      margin-top: 4px;
      text-align: center;
    }

    .struck-math {
      position: relative;
      color: #991b1b;
      display: inline-block;
      font-size: 20px;
    }

    .struck-math::after {
      content: '';
      position: absolute;
      left: -4px;
      right: -4px;
      top: 50%;
      height: 2.5px;
      background: #dc2626;
      transform: rotate(-8deg);
      border-radius: 2px;
    }

    .sub-label {
      font-size: 12px;
      font-weight: 600;
      color: #dc2626;
      margin-top: 6px;
      text-align: center;
    }

    /* Right Column Elements */
    .cards-stack {
      width: 100%;
      display: flex;
      flex-direction: column;
      gap: 8px;
    }

    .card-item {
      background: #ffffff;
      border: 1px solid #bbf7d0;
      border-radius: 8px;
      padding: 8px 10px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      gap: 8px;
      cursor: pointer;
      transition: border-color 0.2s, box-shadow 0.2s;
    }

    .card-item.active {
      border-color: #16a34a;
      box-shadow: 0 0 0 1.5px #16a34a;
    }

    .card-visual {
      display: flex;
      align-items: center;
      gap: 3px;
    }

    .apple-badge {
      position: relative;
      display: inline-flex;
      align-items: center;
      justify-content: center;
    }

    .num-tag {
      position: absolute;
      bottom: -2px;
      right: -2px;
      background: #16a34a;
      color: #fff;
      font-size: 9px;
      font-weight: 800;
      width: 13px;
      height: 13px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      border: 1px solid #fff;
    }

    .price-tag-ui {
      background: #f0fdf4;
      border: 1px dashed #16a34a;
      color: #15803d;
      padding: 3px 6px;
      border-radius: 6px;
      font-size: 12px;
      font-weight: 800;
    }

    .card-info {
      text-align: right;
    }

    .card-eq {
      font-size: 15px;
      font-weight: 700;
      color: #15803d;
    }

    .card-desc {
      font-size: 11px;
      color: #4b5563;
      font-weight: 500;
    }

    /* Bottom takeaway */
    .takeaway {
      background: #1e2945;
      color: #f8fafc;
      padding: 8px 12px;
      border-radius: 8px;
      font-size: 13px;
      font-weight: 600;
      text-align: center;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
    }

    .takeaway span.hl {
      color: #4ade80;
      font-weight: 700;
    }
  </style>
</head>
<body>

  <div class="comparison">
    
    <div class="col col-wrong">
      <div class="badge badge-wrong">✕ NOT an Object</div>
      
      <div class="prohibition-box">
        
        <svg width="68" height="68" viewBox="0 0 64 64">
          
          <path d="M32 18 C32 10 37 6 42 6 C42 12 37 16 32 18 Z" fill="#16a34a"/>
          <path d="M32 18 Q30 11 26 9" stroke="#78350f" stroke-width="2.5" fill="none" stroke-linecap="round"/>
          
          <path d="M32 20 C22 10 10 18 10 34 C10 49 24 58 32 58 C40 58 54 49 54 34 C54 18 42 10 32 20 Z" fill="#ef4444"/>
          
          <path d="M18 26 C15 32 15 40 18 46" stroke="#fca5a5" stroke-width="2.5" fill="none" stroke-linecap="round"/>
        </svg>
        
        <svg class="prohibition-svg" viewBox="0 0 100 100">
          <circle cx="50" cy="50" r="42" stroke="#dc2626" stroke-width="8" fill="none" opacity="0.95"/>
          <line x1="20" y1="20" x2="80" y2="80" stroke="#dc2626" stroke-width="8" stroke-linecap="round" opacity="0.95"/>
        </svg>
      </div>

      <div class="equation-box">
        <span class="struck-math"><span class="var">a</span> = Apple</span>
      </div>
      <div class="sub-label">Variables are not physical items</div>
    </div>

    
    <div class="col col-right">
      <div class="badge badge-right">✓ A Number or Quantity</div>
      
      <div class="cards-stack">
        
        <div class="card-item active" id="cardCount">
          <div class="card-visual">
            <div class="apple-badge">
              <svg width="22" height="22" viewBox="0 0 64 64">
                <path d="M32 20 C22 10 10 18 10 34 C10 49 24 58 32 58 C40 58 54 49 54 34 C54 18 42 10 32 20 Z" fill="#ef4444"/>
              </svg>
              <div class="num-tag">1</div>
            </div>
            <div class="apple-badge">
              <svg width="22" height="22" viewBox="0 0 64 64">
                <path d="M32 20 C22 10 10 18 10 34 C10 49 24 58 32 58 C40 58 54 49 54 34 C54 18 42 10 32 20 Z" fill="#ef4444"/>
              </svg>
              <div class="num-tag">2</div>
            </div>
            <div class="apple-badge">
              <svg width="22" height="22" viewBox="0 0 64 64">
                <path d="M32 20 C22 10 10 18 10 34 C10 49 24 58 32 58 C40 58 54 49 54 34 C54 18 42 10 32 20 Z" fill="#ef4444"/>
              </svg>
              <div class="num-tag">3</div>
            </div>
            <div class="apple-badge">
              <svg width="22" height="22" viewBox="0 0 64 64">
                <path d="M32 20 C22 10 10 18 10 34 C10 49 24 58 32 58 C40 58 54 49 54 34 C54 18 42 10 32 20 Z" fill="#ef4444"/>
              </svg>
              <div class="num-tag">4</div>
            </div>
            <div class="apple-badge">
              <svg width="22" height="22" viewBox="0 0 64 64">
                <path d="M32 20 C22 10 10 18 10 34 C10 49 24 58 32 58 C40 58 54 49 54 34 C54 18 42 10 32 20 Z" fill="#ef4444"/>
              </svg>
              <div class="num-tag">5</div>
            </div>
          </div>
          <div class="card-info">
            <div class="card-eq"><span class="var">a</span> = 5</div>
            <div class="card-desc">Count of apples</div>
          </div>
        </div>

        
        <div class="card-item" id="cardPrice">
          <div class="card-visual">
            <div class="price-tag-ui">🏷️ $1.50</div>
          </div>
          <div class="card-info">
            <div class="card-eq"><span class="var">a</span> = 1.50</div>
            <div class="card-desc">Cost per apple ($)</div>
          </div>
        </div>
      </div>
    </div>
  </div>

  
  <div class="takeaway">
    <span>💡 A variable stands for a <span class="hl">number</span> (count, price, or measure).</span>
  </div>

  <script>
    const c1 = document.getElementById('cardCount');
    const c2 = document.getElementById('cardPrice');

    function selectCard(active, inactive) {
      active.classList.add('active');
      inactive.classList.remove('active');
    }

    c1.addEventListener('click', () => selectCard(c1, c2));
    c2.addEventListener('click', () => selectCard(c2, c1));
  </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;
      color: #1e2945;
      background: #ffffff;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
      padding: 16px;
    }

    .breakdown-container {
      width: 100%;
      max-width: 520px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 16px;
    }

    .header-badge {
      font-size: 16px;
      font-weight: 700;
      color: #1e2945;
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }

    .diagram-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 10px;
      width: 100%;
      flex-wrap: wrap;
    }

    .card-item {
      background: #f8fafc;
      border: 1.5px solid #e2e8f0;
      border-radius: 12px;
      padding: 12px 14px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      gap: 6px;
      transition: box-shadow 0.3s ease, border-color 0.3s ease, background-color 0.3s ease;
      cursor: pointer;
    }

    .card-item:hover, .card-item.active {
      border-color: #22b7ff;
      background: #f0f9ff;
      box-shadow: 0 4px 12px rgba(34, 183, 255, 0.15);
    }

    .icon {
      font-size: 28px;
      line-height: 1;
    }

    .value {
      font-size: 17px;
      font-weight: 700;
      color: #1e2945;
    }

    .operator {
      font-size: 24px;
      font-weight: 800;
      color: #64748b;
    }

    .group-wrapper {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 6px;
      background: #f8fafc;
      border: 1.5px dashed #cbd5e1;
      border-radius: 12px;
      padding: 8px 10px 10px 10px;
      transition: border-color 0.3s ease, background-color 0.3s ease;
    }

    .group-wrapper.active {
      border-color: #22b7ff;
      background: #f0f9ff;
    }

    .group-label {
      font-size: 13px;
      font-weight: 700;
      color: #22b7ff;
      background: #ffffff;
      padding: 2px 8px;
      border-radius: 20px;
      border: 1px solid #22b7ff;
    }

    .drinks-grid {
      display: flex;
      gap: 6px;
    }

    .drink-card {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      padding: 6px 8px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 4px;
      min-width: 44px;
    }

    .drink-card .icon {
      font-size: 20px;
    }

    .drink-card .value {
      font-size: 15px;
    }

    .bottom-banner {
      width: 100%;
      background: #f0f9ff;
      border: 1.5px solid #22b7ff;
      border-radius: 12px;
      padding: 12px 16px;
      text-align: center;
      font-size: 16px;
      font-weight: 600;
      color: #1e2945;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      box-shadow: 0 2px 8px rgba(34, 183, 255, 0.08);
    }

    .expr-highlight {
      font-size: 18px;
      font-weight: 800;
      color: #1e2945;
    }

    .expr-var {
      color: #0284c7;
    }

    .stepper-nav {
      display: flex;
      gap: 8px;
      margin-top: 4px;
    }

    .step-dot {
      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: #cbd5e1;
      border: none;
      cursor: pointer;
      padding: 0;
      transition: background 0.3s ease, transform 0.3s ease;
    }

    .step-dot.active {
      background: #22b7ff;
      transform: scale(1.25);
    }
  </style>
</head>
<body>
  <div class="breakdown-container">
    <div class="header-badge">Total Cost</div>

    <div class="diagram-row">
      <div class="card-item" id="pizzaCard" onclick="setStep(0)">
        <span class="icon">🍕</span>
        <span class="value">$12</span>
      </div>

      <div class="operator">+</div>

      <div class="group-wrapper" id="drinksGroup" onclick="setStep(1)">
        <span class="group-label">4d</span>
        <div class="drinks-grid">
          <div class="drink-card">
            <span class="icon">🥤</span>
            <span class="value">$d</span>
          </div>
          <div class="drink-card">
            <span class="icon">🥤</span>
            <span class="value">$d</span>
          </div>
          <div class="drink-card">
            <span class="icon">🥤</span>
            <span class="value">$d</span>
          </div>
          <div class="drink-card">
            <span class="icon">🥤</span>
            <span class="value">$d</span>
          </div>
        </div>
      </div>
    </div>

    <div class="bottom-banner" id="banner" onclick="setStep(2)">
      <span>Total Expression:</span>
      <span class="expr-highlight">12 + <span class="expr-var">4d</span></span>
    </div>

    <div class="stepper-nav">
      <button class="step-dot active" aria-label="Step 1" onclick="setStep(0)"></button>
      <button class="step-dot" aria-label="Step 2" onclick="setStep(1)"></button>
      <button class="step-dot" aria-label="Step 3" onclick="setStep(2)"></button>
    </div>
  </div>

  <script>
    const pizza = document.getElementById('pizzaCard');
    const drinks = document.getElementById('drinksGroup');
    const banner = document.getElementById('banner');
    const dots = document.querySelectorAll('.step-dot');

    let currentStep = 2;

    function updateView() {
      pizza.classList.toggle('active', currentStep === 0 || currentStep === 2);
      drinks.classList.toggle('active', currentStep === 1 || currentStep === 2);
      banner.style.boxShadow = currentStep === 2 ? '0 4px 14px rgba(34, 183, 255, 0.2)' : 'none';

      dots.forEach((dot, idx) => {
        dot.classList.toggle('active', idx === currentStep);
      });
    }

    function setStep(step) {
      currentStep = step;
      updateView();
    }

    updateView();
  </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 {
      width: 100%;
      height: 100%;
      min-height: 100%;
      background: #ffffff;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 16px;
      user-select: none;
    }

    .diagram {
      width: 100%;
      max-width: 480px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 18px;
    }

    /* Top Badge */
    .badge {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      background: #eff6ff;
      border: 1px solid #bfdbfe;
      color: #1d4ed8;
      padding: 6px 14px;
      border-radius: 9999px;
      font-size: 14px;
      font-weight: 600;
      letter-spacing: 0.2px;
    }

    .badge-var {
      font-style: italic;
      font-weight: 700;
      font-size: 16px;
      color: #2563eb;
    }

    /* Main Visual Row */
    .visual-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 16px;
      width: 100%;
      padding: 8px 0;
    }

    /* Gift Bag */
    .bag-container {
      display: flex;
      flex-direction: column;
      align-items: center;
      position: relative;
    }

    .bag-svg {
      width: 100px;
      height: 110px;
      filter: drop-shadow(0 4px 6px rgba(30, 41, 69, 0.08));
      transition: transform 0.2s ease;
    }

    /* Plus Sign */
    .operator {
      font-size: 32px;
      font-weight: 700;
      color: #94a3b8;
      line-height: 1;
    }

    /* Marbles Group */
    .marbles-group {
      display: flex;
      align-items: center;
      gap: 8px;
      padding: 10px 14px;
      background: #f8fafc;
      border: 1px dashed #cbd5e1;
      border-radius: 14px;
    }

    .marble {
      width: 28px;
      height: 28px;
      border-radius: 50%;
      background: radial-gradient(circle at 32% 28%, #bbf7d0 0%, #22c55e 45%, #15803d 85%, #14532d 100%);
      box-shadow: 0 3px 6px rgba(21, 128, 61, 0.25), inset 0 -2px 4px rgba(0, 0, 0, 0.2);
    }

    /* Equation Box */
    .equation-box {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 10px;
      background: #ffffff;
      border: 1.5px solid #e6e6e6;
      border-radius: 12px;
      padding: 12px 24px;
      box-shadow: 0 2px 8px rgba(30, 41, 69, 0.04);
      font-size: 24px;
      font-weight: 700;
    }

    .eq-label {
      color: #1e2945;
      font-weight: 600;
    }

    .eq-equals {
      color: #64748b;
      margin: 0 2px;
    }

    .eq-var {
      color: #2563eb;
      font-style: italic;
      background: #eff6ff;
      border: 1px solid #dbeafe;
      padding: 2px 10px;
      border-radius: 6px;
    }

    .eq-plus {
      color: #64748b;
    }

    .eq-const {
      color: #16a34a;
      background: #f0fdf4;
      border: 1px solid #dcfce7;
      padding: 2px 10px;
      border-radius: 6px;
    }

    @media (max-width: 380px) {
      .visual-row {
        gap: 10px;
      }
      .bag-svg {
        width: 85px;
        height: 95px;
      }
      .marble {
        width: 24px;
        height: 24px;
      }
      .marbles-group {
        padding: 8px 10px;
        gap: 6px;
      }
      .equation-box {
        font-size: 20px;
        padding: 10px 18px;
      }
      .badge {
        font-size: 13px;
        padding: 5px 12px;
      }
    }
  </style>
</head>
<body>
  <div class="diagram">
    
    <div class="badge">
      <span class="badge-var">m</span> = marbles in the bag
    </div>

    
    <div class="visual-row">
      
      <div class="bag-container">
        <svg class="bag-svg" viewBox="0 0 100 110" fill="none" xmlns="http://www.w3.org/2000/svg">
          
          <path d="M22 36 C22 28 35 26 50 26 C65 26 78 28 78 36 C86 52 90 74 88 92 C86 102 76 106 50 106 C24 106 14 102 12 92 C10 74 14 52 22 36 Z" fill="#3b82f6" />
          <path d="M22 36 C22 28 35 26 50 26 C65 26 78 28 78 36 C86 52 90 74 88 92 C86 102 76 106 50 106 C24 106 14 102 12 92 C10 74 14 52 22 36 Z" fill="url(#bag-shading)" />
          
          
          <path d="M22 36 C20 22 28 14 36 12 C44 20 50 10 50 10 C50 10 56 20 64 12 C72 14 80 22 78 36 Z" fill="#2563eb" />
          
          
          <ellipse cx="50" cy="36" rx="28" ry="4.5" fill="#fbbf24" stroke="#d97706" stroke-width="1.5" />
          <path d="M48 37 Q42 46 40 54" stroke="#d97706" stroke-width="2.5" stroke-linecap="round" fill="none" />
          <path d="M52 37 Q56 47 58 55" stroke="#d97706" stroke-width="2.5" stroke-linecap="round" fill="none" />
          
          
          <rect x="34" y="60" width="32" height="34" rx="8" fill="#ffffff" stroke="#93c5fd" stroke-width="2" />
          <text x="50" y="84" font-family="system-ui, sans-serif" font-size="24" font-weight="bold" font-style="italic" fill="#1d4ed8" text-anchor="middle">m</text>

          
          <defs>
            <linearGradient id="bag-shading" x1="12" y1="26" x2="88" y2="106" gradientUnits="userSpaceOnUse">
              <stop stop-color="#ffffff" stop-opacity="0.25" />
              <stop offset="0.6" stop-color="#1d4ed8" stop-opacity="0" />
              <stop offset="1" stop-color="#1e3a8a" stop-opacity="0.35" />
            </linearGradient>
          </defs>
        </svg>
      </div>

      
      <div class="operator">+</div>

      
      <div class="marbles-group">
        <div class="marble" title="Marble 1"></div>
        <div class="marble" title="Marble 2"></div>
        <div class="marble" title="Marble 3"></div>
      </div>
    </div>

    
    <div class="equation-box">
      <span class="eq-label">Total</span>
      <span class="eq-equals">=</span>
      <span class="eq-var">m</span>
      <span class="eq-plus">+</span>
      <span class="eq-const">3</span>
    </div>
  </div>
</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;
      color: #1e2945;
      background: #ffffff;
      padding: 16px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
    }
    .wrapper {
      width: 100%;
      max-width: 580px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 20px;
    }
    .cards-container {
      width: 100%;
      display: flex;
      gap: 16px;
      justify-content: center;
      align-items: stretch;
    }
    .side-card {
      flex: 1;
      background: #f8fafc;
      border: 2px solid #e2e8f0;
      border-radius: 14px;
      padding: 18px 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      text-align: center;
      position: relative;
      transition: border-color 0.3s ease, background-color 0.3s ease;
    }
    .side-card.algebra {
      background: #f0f9ff;
      border-color: #22b7ff;
    }
    .tag {
      font-size: 13px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.05em;
      color: #64748b;
      margin-bottom: 14px;
    }
    .algebra .tag {
      color: #0284c7;
    }
    .equation {
      font-size: 26px;
      font-weight: 700;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      color: #1e2945;
    }
    .placeholder-box {
      width: 42px;
      height: 42px;
      border: 2px dashed #94a3b8;
      border-radius: 8px;
      display: inline-flex;
      align-items: center;
      justify-content: center;
      background: #ffffff;
      color: #0284c7;
      font-weight: 700;
      font-size: 22px;
      transition: all 0.3s ease;
    }
    .var-symbol {
      width: 42px;
      height: 42px;
      border: 2px solid #22b7ff;
      border-radius: 8px;
      display: inline-flex;
      align-items: center;
      justify-content: center;
      background: #ffffff;
      color: #0284c7;
      font-style: italic;
      font-weight: 700;
      font-size: 24px;
      box-shadow: 0 2px 8px rgba(34, 183, 255, 0.2);
      transition: all 0.3s ease;
    }
    .callout {
      margin-top: 14px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 2px;
    }
    .arrow-up {
      color: #0284c7;
      font-size: 16px;
      line-height: 1;
    }
    .badge {
      background: #22b7ff;
      color: #ffffff;
      font-size: 12px;
      font-weight: 700;
      padding: 4px 10px;
      border-radius: 20px;
      white-space: nowrap;
    }
    .sub-label {
      font-size: 11px;
      color: #475569;
      font-weight: 600;
      margin-top: 2px;
    }
    .action-btn {
      background: #1e2945;
      color: #ffffff;
      border: none;
      padding: 10px 22px;
      font-size: 14px;
      font-weight: 600;
      border-radius: 24px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 8px;
      transition: background 0.2s ease, opacity 0.2s ease;
    }
    .action-btn:hover {
      background: #0f172a;
    }
    .action-btn:active {
      opacity: 0.9;
    }

    @media (max-width: 420px) {
      .equation {
        font-size: 21px;
        gap: 6px;
      }
      .placeholder-box, .var-symbol {
        width: 36px;
        height: 36px;
        font-size: 19px;
      }
      .side-card {
        padding: 14px 8px;
      }
    }
  </style>
</head>
<body>
  <div class="wrapper">
    <div class="cards-container">
      
      <div class="side-card">
        <span class="tag">Elementary</span>
        <div class="equation">
          <span class="placeholder-box" id="boxElem">□</span>
          <span>+</span>
          <span>5</span>
          <span>=</span>
          <span>12</span>
        </div>
      </div>

      
      <div class="side-card algebra">
        <span class="tag">Algebra</span>
        <div class="equation">
          <span class="var-symbol" id="boxAlg">x</span>
          <span>+</span>
          <span>5</span>
          <span>=</span>
          <span>12</span>
        </div>
        <div class="callout">
          <span class="arrow-up">▲</span>
          <span class="badge">Variable</span>
          <span class="sub-label">Unknown number</span>
        </div>
      </div>
    </div>

    
    <button class="action-btn" id="toggleBtn" onclick="toggleSolve()">
      <span id="btnIcon">✦</span>
      <span id="btnText">Reveal Unknown</span>
    </button>
  </div>

  <script>
    let solved = false;
    function toggleSolve() {
      solved = !solved;
      const boxElem = document.getElementById('boxElem');
      const boxAlg = document.getElementById('boxAlg');
      const btnText = document.getElementById('btnText');

      if (solved) {
        boxElem.textContent = '7';
        boxElem.style.borderColor = '#22b7ff';
        boxElem.style.borderStyle = 'solid';
        boxElem.style.background = '#e0f2fe';

        boxAlg.textContent = '7';
        boxAlg.style.fontStyle = 'normal';
        boxAlg.style.background = '#e0f2fe';

        btnText.textContent = 'Reset';
      } else {
        boxElem.textContent = '□';
        boxElem.style.borderColor = '#94a3b8';
        boxElem.style.borderStyle = 'dashed';
        boxElem.style.background = '#ffffff';

        boxAlg.textContent = 'x';
        boxAlg.style.fontStyle = 'italic';
        boxAlg.style.background = '#ffffff';

        btnText.textContent = 'Reveal Unknown';
      }
    }
  </script>
</body>
</html>

OGM.6.OA.2

Aligned learning resources

Related diagrams