CodePen

HTML

            
              <table>
  <tr>
    <td>00</td>
    <td>15</td>
    <td>20</td>
    <td>45</td>
    <th>5</th>
    <td>00</td>
    <td>20</td>
    <td>30</td>
    <td>45</td>
  </tr>
  
  <tr>
    <td></td>
    <td></td>
    <td>20</td>
    <td>45</td>
    <th>6</th>
    <td>00</td>
    <td>30</td>
    <td></td>
    <td></td>
  </tr>
  
  <tr>
    <td></td>
    <td></td>
    <td></td>
    <td>45</td>
    <th>7</th>
    <td>20</td>
    <td>30</td>
    <td>45</td>
    <td></td>
  </tr>
  
  <tr>
    <td></td>
    <td></td>
    <td></td>
    <td></td>
    <th>8</th>
    <td>00</td>
    <td></td>
    <td></td>
    <td></td>
  </tr>
</table>

            
          
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CSS

            
              table {
  border-collapse: collapse;
}

th {
  border-left  : solid black;
  border-right : solid black;
}

            
          
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