code: function loadCss() {
      var cssFileName = fs.path.join(fs.knownFolders.currentApp().path, application.cssFile);
  
      var applicationCss;
      if (FSA.fileExists(cssFileName)) {
          FSA.readText(cssFileName, function (r) { applicationCss = r; });
          //noinspection JSUnusedAssignment
          application.cssSelectorsCache = styleScope.StyleScope.createSelectorsFromCss(applicationCss, cssFileName);
  
          // Add New CSS to Current Page
          var f = frameCommon.topmost();
          if (f && f.currentPage) {
              f.currentPage._resetCssValues();
              f.currentPage._styleScope = new styleScope.StyleScope();
              //noinspection JSUnusedAssignment
              f.currentPage._addCssInternal(applicationCss, cssFileName);
              f.currentPage._refreshCss();
          }
      }
  }
docs: This is the loadCss helper function to replace the one on Application