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

<select class="form-select form-select-lg mb-3" aria-label=".form-select-lg example">
  <option selected>Open this select menu</option>
  <option value="1">One</option>
  <option value="2">Two</option>
  <option value="3">Three</option>
</select>

<select class="form-select form-select-sm" aria-label=".form-select-sm example">
  <option selected>Open this select menu</option>
  <option value="1">One</option>
  <option value="2">Two</option>
  <option value="3">Three</option>
</select>

<select class="form-select" id="multiple-select-field" name="Multiple Select" multiple>
  <option>Christmas Island</option>
  <option>South Sudan</option>
  <option>Jamaica</option>
  <option>Kenya</option>
  <option>French Guiana</option>
  <option>Mayotta</option>
  <option>Liechtenstein</option>
  <option>Denmark</option>
  <option>Eritrea</option>
  <option>Gibraltar</option>
  <option>Saint Helena, Ascension and Tristan da Cunha</option>
  <option>Haiti</option>
  <option>Namibia</option>
  <option>South Georgia and the South Sandwich Islands</option>
  <option>Vietnam</option>
  <option>Yemen</option>
  <option>Philippines</option>
  <option>Benin</option>
  <option>Czech Republic</option>
  <option>Russia</option>
</select>

$('#multiple-select-field').select2({
  placeholder: "Select your lists" // show a placeholder
});