Code reproduce :

@Override
    public void start(Stage stage) throws Exception {
        BorderPane root = new BorderPane();
        
        final DatePicker picker = new DatePicker();
        
        ScheduledExecutorService service = Executors.newScheduledThreadPool(1);
        service.schedule(new Runnable() {

            @Override
            public void run() {
                Platform.runLater(new Runnable() {

                    @Override
                    public void run() {
                        picker.setStyle("-fx-border-width:10;-fx-border-color:red;");
                        System.out.println("Set border.");
                    }
                });
            }
        }, 8, TimeUnit.SECONDS);
        root.setCenter(picker);
        Scene scene = new Scene(root, 600, 300);
        stage.setScene(scene);
        stage.setTitle(VersionInfo.getRuntimeVersion());
        stage.show();
    }