<table class='parent'>
  <tr>
    <th>head</th>
    <th>head</th>
    <th>Description</th>
    <th>
      <table>
        <tr>
            <th>head</th>
            <th>head</th>
            <th>head</th>
            <th>head</th>
        </tr>
      </table>
    </th>
  </tr>
  <tr>
    <td>values</td>
    <td>values</td>
    <td>Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, Description goes here, </td>
    <td>
      <table class='inner'>
          <tbody>
            <tr>
              <td>H1 Val</td>
              <td>H2 Val</td>
              <td>H3 Val</td>
              <td>H4 Val</td>
            </tr>
          </tbody>
      </table>
    </td>
  </tr>
</table>

.parent{
  border:1px solid #000;
  border-collapse:collapse;
}
.parent td, .parent tr, .parent th{
  border:1px solid #000;
}

.inner{
  height:100%;
}