Select: Error

<div class="au-form__item">
    <label for="favourite">
        Favourite animal
        <span class="form-required">(mandatory)</span> </label>
    <select class="au-select error" id="favourite">
        <option>Dinosaurs</option>
        <option>Birds</option>
        <option>Mammals</option>
    </select>
</div>