When if open pane content - shadow not visible.
@Override
    public void start(Stage stage) throws Exception {
        BorderPane root = new BorderPane();
        final Accordion pane = new Accordion();
        pane.getPanes().add(new TitledPane("Title 1", new Label("Test")));
        pane.getPanes().add(new TitledPane("Title 2", new Label("Test 2")));
        pane.getPanes().get(0).setCollapsible(true);
        pane.setStyle(style);
        pane.setPrefSize(100, 100);
        pane.setMaxSize(100, 100);
        root.setCenter(HBoxBuilder.create().spacing(15).children(pane).build());
        Scene scene = new Scene(root, 400, 400);
        stage.setScene(scene);
        stage.show();
    }