code: public static Runnable start(Stage stage) {
          CSSFXConfig cfg = new CSSFXConfig();
          cfg.setRestrictedToStage(stage);
          return cfg.start();
      }
docs: Directly start monitoring CSS for the given Stage.
  <ul>
  <li>standard source file detectors: Maven, Gradle, execution from built JAR (details in {@link URIToPathConverters#DEFAULT_CONVERTERS})</li>
  <li>detection activated on the stage only (and its children)</li>
  </ul>
  @param stage the stage that will be monitored
  @return a Runnable object to stop CSSFX monitoring