public void init() { previousButtonStackPane.setOnMouseExited( new EventHandler<MouseEvent>() { @Override public void handle(MouseEvent mouseEvent) { previousButton.setFitHeight(50); previousButton.setFitWidth(50); } }); previousButtonStackPane.setOnMouseEntered( new EventHandler<MouseEvent>() { @Override public void handle(MouseEvent mouseEvent) { previousButton.setFitHeight(60); previousButton.setFitWidth(60); } }); }