<style>
  table {
    border-collapse: collapse;
  }

  td {
    border: 1px solid black;
    padding: 10px 20px;
  }

  .td-thick-border {
    border: 5px solid black;
  }
</style>

<table>
  <tbody>
    <tr class="td-thick-border">
      <td>A</td>
      <td>B</td>
    </tr>
    <tr>
      <td>C</td>
      <td>D</td>
    </tr>
    <tr class="td-thick-border">
      <td>E</td>
      <td>F</td>
    </tr>
  </tbody>
</table>