src/widget/Box.php
protected function renderFooter()
    {
        if ($this->footer !== null) {
            $content = $this->footer;
            if($this->usebutton){
                $content .= $this->renderButton(self::POSITION_FOOTER);
            }
            return Html::tag('div', "\n" . $content . "\n", ['class' => 'box-footer clearfix']);            
        } else {
            return null;
        }
    }
protected function renderFooter()
    {
        if ($this->footer !== null) {
            $content = $this->footer;
            if($this->usebutton){
                $content .= $this->renderButton(self::POSITION_FOOTER);
            }
            return Html::tag('div', "\n" . $content . "\n", ['class' => 'box-footer clearfix']);            
        } else {
            return null;
        }
    }
Renders the HTML markup for the footer of the modal
@return string the rendering result