Custom UI

Form - Select

Select simple (con estados)

html 
<select>
  <option value="option1">Option 1</option>
  <option value="option2" selected>Option 2</option>
  <option value="option3">Option 3</option>
  <option value="option4">Option 4</option>
</select>
<select class="is-valid">
  <option value="option1">Option 1</option>
  <option value="option2" selected>Option 2</option>
  <option value="option3">Option 3</option>
  <option value="option4">Option 4</option>
</select>
<select class="is-invalid">
  <option value="option1">Option 1</option>
  <option value="option2" selected>Option 2</option>
  <option value="option3">Option 3</option>
  <option value="option4">Option 4</option>
</select>
<select disabled>
  <option value="option1">Option 1</option>
  <option value="option2" selected>Option 2</option>
  <option value="option3">Option 3</option>
  <option value="option4">Option 4</option>
</select>

Select múltiple (con estados)

html 
<select multiple>
  <option value="option1">Option 1</option>
  <option value="option2" selected>Option 2</option>
  <option value="option3">Option 3</option>
  <option value="option4">Option 4</option>
</select>
<select multiple class="is-valid">
  <option value="option1">Option 1</option>
  <option value="option2" selected>Option 2</option>
  <option value="option3">Option 3</option>
  <option value="option4">Option 4</option>
</select>
<select multiple class="is-invalid">
  <option value="option1">Option 1</option>
  <option value="option2" selected>Option 2</option>
  <option value="option3">Option 3</option>
  <option value="option4">Option 4</option>
</select>
<select multiple disabled>
  <option value="option1">Option 1</option>
  <option value="option2" selected>Option 2</option>
  <option value="option3">Option 3</option>
  <option value="option4">Option 4</option>
</select>