<!-- Center table in page -->
<TABLE class="w3-table w3-striped w3-bordered w3-border w3-white" align="center">
...
</table>

<!-- Center content of table -->
<div style="overflow-x:auto;">
<TABLE class="w3-table w3-striped w3-bordered w3-border w3-white">
  <thead style="text-align:center">
    <tr>
      <th>...</th>
    </tr>
  </thead>
  <tbody style="text-align:center">
    <tr>
      <th>...</th>
    </tr>
  </tbody>
</table>

.centerTable { margin: 0px auto; }