  <button class="key" type="button">2</button>
          </div>
          <div class="pad__slot r3 c2">
            <button class="key" type="button">3</button>
          </div>
          <div class="pad__slot r3 c3 rowspan2">
            <button class="key key--secondary" type="button">=</button>
          </div>

          <div class="pad__slot r4 c0 colspan2">
            <button class="key" type="button">0</button>
          </div>
          <div class="pad__slot r4 c2">
            <button class="key" 