code: protected function renderButtons()
      {
          $buttons = [];
          foreach ($this->buttons as $button) {
              if (is_array($button)) {
                  if(isset($button['dropdown'])){
                      $option = array_merge($button['dropdown'], [
                          'view' => $this->getView()
                      ]);
                      $buttons[] = ButtonDropdown::widget($option);
                  }else{
                      $label = ArrayHelper::getValue($button, 'label');
                      $options = ArrayHelper::getValue($button, 'options');
                      $buttons[] = Button::widget([
                          'label' => $label,
                          'options' => $options,
                          'encodeLabel' => $this->encodeLabels,
                          'view' => $this->getView()
                      ]);
                  }
              } else {
                  $buttons[] = $button;
              }
          }
  
          return implode("\n", $buttons);
      }
docs: Generates the buttons that compound the group as specified on [[buttons]].
  @return string the rendering result.