.col-group-1 {
  background-color: yellow;
 }

.col-group-2 {
  background-color: silver;
 }

<table>
  <colgroup>
    <col class="col-group-1">
    <col span="2" class="col-group-2">
  </colgroup>
  <tr>
    <th>Name</th>
    <th>City</th>
    <th>Phone</th>
  </tr>
  <tr>
    <td>Mary</td>
    <td>New york</td>
    <td>987654321</td>
  </tr>
  <tr>
    <td>Magdalena</td>
    <td>Los Angeles</td>
    <td>123456789</td>
  </tr>
</table>

</body>
</html>

请查看html col tag

以及如何使用它们与css styling