code: public static Resource getSmallIconResource(CmsExplorerTypeSettings explorerType, String resourceName) {
  
          if (explorerType == null) {
              explorerType = OpenCms.getWorkplaceManager().getExplorerTypeSetting(
                  (resourceName == null) && !CmsResource.isFolder(resourceName)
                  ? CmsResourceTypeUnknownFile.RESOURCE_TYPE_NAME
                  : "unknown_folder");
          }
  
          if (!explorerType.getIconRules().isEmpty() && (resourceName != null)) {
              String extension = CmsResource.getExtension(resourceName);
              if (extension != null) {
                  CmsIconRule rule = explorerType.getIconRules().get(extension);
                  if ((rule != null) && (rule.getSmallIconStyle() != null)) {
                      return new CmsCssIcon(rule.getSmallIconStyle());
                  }
              }
          }
          if (explorerType.getSmallIconStyle() != null) {
              return new CmsCssIcon(explorerType.getSmallIconStyle());
          } else {
              return new ExternalResource(
                  CmsWorkplace.getResourceUri(CmsWorkplace.RES_PATH_FILETYPES + explorerType.getOriginalIcon()));
          }
      }
docs: Returns the small icon resource for the given resource.<p>
  
  @param explorerType the resource explorer type settings
  @param resourceName the resource name
  
  @return the icon resource