<!-- form select -->
<select class="form-select">
  <option selected>Open this select menu</option>
  <option value="1">One</option>
  <option value="2">Two</option>
  <option value="3">Three</option>
</select>

<!-- form-select-lg -->
<select class="form-select form-select-lg">...</select>

<!-- form-select-sm -->
<select class="form-select form-select-sm">...</select>