You can do that but not with simple CSS.

Your select would have to look something like that:

<section class="d-flex">
<!-- set width to this div -->
  <div class="width: 200px">
    <select class="select">
      <option value="1">One</option>
      <option value="2">Two</option>
      <option value="3">Three</option>
      <option value="4">Four</option>
      <option value="5">Five</option>
      <option value="6">Six</option>
      <option value="7">Seven</option>
      <option value="8">Eight</option>
    </select>
  </div>
</section>

and you would have to write JS code that will calculate the width of the widest option and set it (with some additional width for padding and arrow) to div that I've marked above. It can result in some page shifting on initial loading.