ButtonDropdown with primary class


I’m trying to display a dropdown with success class, as shown in Bootstrap demo.

The code is the following:

        echo ButtonDropdown::widget([

            'label' => Yii::t('gestical', 'Nuova'),

            'options' => ['class' => 'btn btn-success'],

            'dropdown' => [

                'items' => $opz,



but the button is displayed in gray color. I checked the source and the html is the following:

<button id="w1" class="btn btn-success dropdown-toggle ui-button ui-widget ui-state-default ui-corner-all ui-button-text-only" data-toggle="dropdown" role="button"><span class="ui-button-text">Nuova <span class="caret"></span></span></button>

so the problem is that class ui-state-default overrides the background color set by btn-success. Have I used the wrong class or is it a bug? thanks