See attached screenshot. Slider should have the same height as the rectangle.

Code snippet:

Group root = new Group();
Scene scene = new Scene(root, 500, 500);
        
Rectangle rectangle = new Rectangle(100, 100);
rectangle.setLayoutX(50);
rectangle.setLayoutY(50);
        
Slider slider = new Slider();
slider.setOrientation(Orientation.VERTICAL);
slider.setPrefHeight(100);
slider.setPrefWidth(15);
slider.setLayoutX(200);
slider.setLayoutY(50);
        
root.getChildren().addAll(rectangle, slider);
stage.setScene(scene);
stage.setVisible(true);