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);
          }
        });
  }