src/widget/Box.php
protected function initDefaultButtons()
    {
        if (!isset($this->buttons['collapse'])) {
            $this->buttons['collapse'] = function ($option) {
                $option['class'] = 'btn '.$option['class'];
                $option['data-widget'] = 'collapse';
                $option['data-toggle'] = 'tooltip';
                $option['title'] = Yii::t('yii', 'Collapse');
                
                if($option['notitle']){
                    unset($option['notitle'],$option['title']);
                }
                
                return Html::tag('button','<i class="fa fa-minus"></i>', $option);
            };
        }
        if (!isset($this->buttons['remove'])) {
            $this->buttons['remove'] = function ($option) {
                $option['class'] = 'btn '.$option['class'];
                $option['data-widget'] = 'remove';
                $option['data-toggle'] = 'tooltip';
                $option['title'] = Yii::t('yii', 'Remove');
                
                if($option['notitle']){
                    unset($option['notitle'],$option['title']);
                }
                return Html::tag('button','<i class="fa fa-times"></i>', $option);
            };
        }        
    }
protected function initDefaultButtons()
    {
        if (!isset($this->buttons['collapse'])) {
            $this->buttons['collapse'] = function ($option) {
                $option['class'] = 'btn '.$option['class'];
                $option['data-widget'] = 'collapse';
                $option['data-toggle'] = 'tooltip';
                $option['title'] = Yii::t('yii', 'Collapse');
                
                if($option['notitle']){
                    unset($option['notitle'],$option['title']);
                }
                
                return Html::tag('button','<i class="fa fa-minus"></i>', $option);
            };
        }
        if (!isset($this->buttons['remove'])) {
            $this->buttons['remove'] = function ($option) {
                $option['class'] = 'btn '.$option['class'];
                $option['data-widget'] = 'remove';
                $option['data-toggle'] = 'tooltip';
                $option['title'] = Yii::t('yii', 'Remove');
                
                if($option['notitle']){
                    unset($option['notitle'],$option['title']);
                }
                return Html::tag('button','<i class="fa fa-times"></i>', $option);
            };
        }        
    }
Initializes the default button rendering callbacks