code: protected void addCSS(final Scene scene, final StyleSheetItem styleSheetItem) {
  
          final URL styleSheetURL = styleSheetItem.get();
          if (styleSheetURL == null) {
              LOGGER.error(CSS_LOADING_ERROR, styleSheetItem.toString(), ResourceParameters.STYLE_FOLDER.get());
          } else {
              scene.getStylesheets().add(styleSheetURL.toExternalForm());
          }
  
      }
docs: Attach a new CSS file to the scene using the default classloader.
  
  @param scene the scene that will hold this new CSS file
  @param styleSheetItem the stylesheet item to add