JavaFx button style - css

Question

I have problem to add style to button controll from external css file,I trying something like this,example button.getStyleSheets().add(".../... .css");
I trying to select one button controll,not multiple buttons.I think to set style to button from external css file,and I would change code somewhere to works(I can fix that,over ObservableLis list=button.getStyleSheets(); .......) but I can't add external file to button.
//when I click left mouse button,selected them and if I type delete key delete him
else if(e.getButton() == MouseButton.PRIMARY && e.getClickCount() == 1)
{
//Ako se stisne taster delete da se izbrise dobavljac
universal_dobavljac.addEventHandler(KeyEvent.KEY_PRESSED, (ee) ->{
if(ee.getCode() == KeyCode.DELETE)
{
//Potvrda za brisanje dobavljača
ButtonType da=new ButtonType("Da", ButtonBar.ButtonData.OK_DONE);
ButtonType ne=new ButtonType("Ne", ButtonBar.ButtonData.CANCEL_CLOSE);
Alert alert=new Alert(Alert.AlertType.CONFIRMATION,"Da li želite da obrišete "+dob.getNaziv_firme()+ " dobavljača?",da,ne);
alert.setHeaderText(null);
Optional<ButtonType> result=alert.showAndWait();
if(result.isPresent() && result.get() == da)
{
//brisanje iz tilepane
tilePane.getChildren().remove(universal_dobavljac);
//brisanje dobavljaca iz baze
try{
transaction=session.beginTransaction();
session.delete(dob);
transaction.commit();
}
catch(HibernateException ex)
{
if(transaction != null)
{
transaction.rollback();
}
}
Alert alertt=new Alert(Alert.AlertType.INFORMATION);
alertt.setHeaderText(null);
alertt.setContentText("Uspešno ste izbrisali "+dob.getNaziv_firme()+" dobavljača");
alertt.show();
}
}
});
////////////////
//THIS comments bellow don't works -> Path is good,I check at least hundred times
//universal_dobavljac.getStylesheets().add(getClass().getResource("Finansije/Dobavljaci/kada_je_selektovan_dobavljac.css").toExternalForm());
universal_dobavljac.setStyle("-fx-font-weight: bold; -fx-font-size: 36px; -fx-font-family: Book Antiqua; -fx-pref-width: 303px; -fx-pref-height: 230px; -fx-background-image: url(\"Finansije/icon_hover.png\"); -fx-background-color: transparent; -fx-cursor: hand");
universal_dobavljac.addEventHandler(MouseEvent.MOUSE_EXITED,(event) ->{
//universal_dobavljac.getStylesheets().add(getClass().getResource("Finansije/Dobavljaci/kada_je_selektovan_dobavljac.css").toExternalForm());
universal_dobavljac.setStyle("-fx-font-weight: bold; -fx-font-size: 36px; -fx-font-family: Book Antiqua; -fx-pref-width: 303px; -fx-pref-height: 230px; -fx-background-image: url(\"Finansije/icon_hover.png\"); -fx-background-color: transparent; -fx-cursor: hand");
});
}
The problem is down bellow.