The size of the content will be the same as that of its ScrollPane container.

import javafx.scene.control.ScrollPane;   //Import the ScrollPane
import javafx.scene.control.ScrollPane.ScrollBarPolicy; //Import the ScrollBarPolicy
import javafx.scene.layout.Pane;

ScrollPane scrollpane;
Pane content = new Pane();  //We will use this Pane as a content

scrollpane = new ScrollPane(content);  //Initialize and add content as a parameter
scrollpane.setPrefSize(300, 300);   //Initialize the size of the ScrollPane

scrollpane.setFitToWidth(true);  //Adapt the content to the width of ScrollPane
scrollpane.setFitToHeight(true); //Adapt the content to the height of ScrollPane


scrollpane.setHbarPolicy(ScrollBarPolicy.ALWAYS);  //Control the visibility of the Horizontal ScrollBar
scrollpane.setVbarPolicy(ScrollBarPolicy.NEVER);  //Control the visibility of the Vertical ScrollBar
//There are three types of visibility (ALWAYS/AS_NEEDED/NEVER)

The size of the content will change depending on the added elements that exceed the content limits in both axes (horizontal and vertical) that can be seen by moving through the view.

import javafx.scene.control.ScrollPane;   //Import the ScrollPane
import javafx.scene.control.ScrollPane.ScrollBarPolicy; //Import the ScrollBarPolicy
import javafx.scene.layout.Pane;

ScrollPane scrollpane;
Pane content = new Pane();  //We will use this Pane as a content

scrollpane = new ScrollPane();  
scrollpane.setPrefSize(300, 300);   //Initialize the size of the ScrollPane
content.setMinSize(300,300); //Here a minimum size is set so that the container can be extended.
scrollpane.setContent(content); // we add the content to the ScrollPane

Note : Here we don't need both methods (setFitToWidth/setFitToHeight).

The appearance of the ScrollPane can be easily changed, by having some notions of "CSS" and respecting some control "properties" and of course having some "imagination".

A) The elements that make up ScrollPane :

B) CSS properties :

.scroll-bar:vertical .track{}

.scroll-bar:horizontal .track{}

.scroll-bar:horizontal .thumb{}

.scroll-bar:vertical .thumb{}


.scroll-bar:vertical *.increment-button,
.scroll-bar:vertical *.decrement-button{}

.scroll-bar:vertical *.increment-arrow .content, 
.scroll-bar:vertical *.decrement-arrow .content{}

.scroll-bar:vertical *.increment-arrow, 
.scroll-bar:vertical *.decrement-arrow{}


.scroll-bar:horizontal *.increment-button,
.scroll-bar:horizontal *.decrement-button{}

.scroll-bar:horizontal *.increment-arrow .content, 
.scroll-bar:horizontal *.decrement-arrow .content{}

.scroll-bar:horizontal *.increment-arrow, 
.scroll-bar:horizontal *.decrement-arrow{}

.scroll-pane .corner{}

.scroll-pane{}