yii\bootstrap\Tabs::init PHP Method

    public function init()
    {
        parent::init();
        Html::addCssClass($this->options, ['widget' => 'nav', $this->navType]);
    }

 /**
  * Initializes the widget.
  */
 public function init()
 {
     if ($this->justified) {
         Html::addCssClass($this->options, 'nav-justified');
     }
     Html::addCssClass($this->options, 'nav ' . $this->navType);
     parent::init();
 }