src/widget/Box.php
protected function renderHeader()
    {
        if ($this->header !== null) {
            $content = '';
            if($this->headerIcon !== null){
               $content .=  Html::tag('i', '', ['class' => $this->headerIcon]);
            }
            
            $content .=  Html::tag('h3', "\n" . $this->header . "\n", ['class' => 'box-title']);
            
            if($this->headerButton !== null){
               $content .=  Html::tag('div', $this->headerButton, ['class' => ($this->headerButtonGroup) ? 'pull-right box-tools btn-group':'pull-right box-tools']);
            }
            
            if($this->usebutton){
                $content .= $this->renderButton(self::POSITION_HEADER);
            }
            
            return Html::tag('div', $content, array_merge(['class' => 'box-header'],  $this->headeroption));
        } else {
            return null;
        }
    }
protected function renderHeader()
    {
        if ($this->header !== null) {
            $content = '';
            if($this->headerIcon !== null){
               $content .=  Html::tag('i', '', ['class' => $this->headerIcon]);
            }
            
            $content .=  Html::tag('h3', "\n" . $this->header . "\n", ['class' => 'box-title']);
            
            if($this->headerButton !== null){
               $content .=  Html::tag('div', $this->headerButton, ['class' => ($this->headerButtonGroup) ? 'pull-right box-tools btn-group':'pull-right box-tools']);
            }
            
            if($this->usebutton){
                $content .= $this->renderButton(self::POSITION_HEADER);
            }
            
            return Html::tag('div', $content, array_merge(['class' => 'box-header'],  $this->headeroption));
        } else {
            return null;
        }
    }
Renders the header HTML markup of the modal
@return string the rendering result