.my-table {

    border: 2px solid black;

    border-collapse: collapse;

}

​

.my-table td {

    border: 1px solid black;

    padding: 5px;

}

​

.colspan-2 {

    grid-column: span 2;

}

<table>

  <tr>

    <th>Month</th>

    <th>Savings</th>

  </tr>

  <tr>

    <td>January</td>

    <td>$100</td>

  </tr>

  <tr>

    <td>February</td>

    <td>$80</td>

  </tr>

  <tr>

    <td colspan="2">Sum: $180</td>

  </tr>

</table>