code: public void addStyleSheetProperties(Content head) {
          String stylesheetfile = configuration.stylesheetfile;
          DocPath stylesheet;
          if (stylesheetfile.isEmpty()) {
              stylesheet = DocPaths.STYLESHEET;
          } else {
              DocFile file = DocFile.createFileForInput(configuration, stylesheetfile);
              stylesheet = DocPath.create(file.getName());
          }
          HtmlTree link = HtmlTree.LINK("stylesheet", "text/css",
                  pathToRoot.resolve(stylesheet).getPath(),
                  "Style");
          head.addContent(link);
          if (configuration.createindex) {
              HtmlTree jq_link = HtmlTree.LINK("stylesheet", "text/css",
                      pathToRoot.resolve(DocPaths.JQUERY_FILES.resolve(DocPaths.JQUERY_STYLESHEET_FILE)).getPath(),
                      "Style");
              head.addContent(jq_link);
          }
      }
docs: Add a link to the stylesheet file.
  
  @param head the content tree to which the files will be added