code: public function init()
      {
          Html::addCssClass($this->options, ['panel', 'sx-panel', $this->color]);
  
          $options = ArrayHelper::merge($this->options, [
              'id' => $this->id,
          ]);
  
          echo Html::beginTag('div', $options);
  
          echo Html::beginTag('div', $this->headingOptions);
  
          echo <<<HTML
  
                  <div class="pull-left">
                      <h2>
                          {$this->name}
                      </h2>
                  </div>
                  <div class="panel-actions panel-hidden-actions">
                      {$this->actions}
                  </div>
  HTML;
  
          echo Html::endTag('div');
  
          echo Html::beginTag('div', $this->bodyOptions);
  
          //echo '<div class="panel-content">' . $this->content;
          echo $this->content;
  
      }
docs: Initializes the widget.
  This renders the form open tag.