code: protected function renderSides($sides)
      {
          $lines = [];
          $lines[] = Html::beginTag('div', $this->sidesOptions);
          foreach($sides as $side) {
              if(!array_key_exists('content', $side)) {
                  throw new InvalidConfigException("The 'content' option is required per sides");
              }
              $options = ArrayHelper::getValue($side, 'options', []);
              Ui::addCssClass($options, 'side');
              $active = ArrayHelper::getValue($side, 'active', false);
              if($active === true) {
                  Ui::addCssClass($options, 'active');
              }
              $lines[] = Html::tag('div', $side['content'], $options);
  
          }
          $lines[] = Html::endTag('div');
  
          return implode("\n", $lines);
      }
docs: Renders the configured sides
  
  @param array $sides @see $sides
  
  @return string the generated shape sides
  @throws InvalidConfigException