JavaFX: load css from file

• load from relative path:

   // the java class is in the same directory as the .css file.
  String css = getClass().getResource("MyApp.css").toExternalForm();
  scene.getStyleSheets().add(css);
  

• load from absolute path:

  // the .css file is stored under <ROOT>/css/ directory.
  String css = getClass().getResource("css/MyApp.css").toExternalForm(); 
  scene.getStyleSheets().add(css);