<!DOCTYPE html>
<style>
.flex-item {
  flex: 1 1 ;
}
</style>
<div style="display: flex">
  <div class="flex-item">y</div>
  <div class="flex-item">
    <table>
      <tr style="background-color: red">
        <td>
          x
        </td>
      </tr>
    </table>
  </div>
</div>