工作需要，研究了一下 ScrollPane，先上图感受：

import javafx.application.Application;
import javafx.application.Platform;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.value.ObservableValue;
import javafx.geometry.Insets;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.ScrollBar;
import javafx.scene.control.ScrollPane;
import javafx.scene.layout.Background;
import javafx.scene.layout.BackgroundFill;
import javafx.scene.layout.CornerRadii;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

public class ScrollPaneTest extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) {
        ScrollPane scrollPane = new ScrollPane();
        scrollPane.setPrefHeight(300);
        scrollPane.setPrefWidth(300);
        // ScrollPane的背景色会被上层覆盖，即使content内容为null
        scrollPane.setBackground(new Background(new BackgroundFill(Color.rgb(12,40,60), new CornerRadii(0), new Insets(0))));
        StackPane stackPane = new StackPane();
        stackPane.setPrefHeight(300);
        stackPane.setPrefWidth(300);
        stackPane.setPadding(new Insets(10));
        // 推荐使用StyleSheets，默认scrollbar.css和本类同级，如果有资源文件夹resources，放resources里
        scrollPane.getStylesheets().add("scrollbar.css");
        stackPane.setBackground(new Background(new BackgroundFill(Color.rgb(12,40,60), new CornerRadii(0), new Insets(0))));
        // 设置流程图整体高度变化后垂直滚动到底，使纵向新增节点及时显示
        stackPane.heightProperty().addListener((ObservableValue<? extends Number> observable, Number oldValue, Number newValue) -> scrollPane.setVvalue(1));
        // 如果在较长时间逻辑执行后，设置水平滚动条，推荐:Platform.runLater(() -> scrollPane.setHvalue(finalHorizontalScroll));
        double finalHorizontalScroll = 0.5;
        scrollPane.setHvalue(finalHorizontalScroll);

        /*Platform.runLater(() -> {
            // 无法解决横向滚动条的问题
            ScrollBar horizontalScrollBar = (ScrollBar)scrollPane.lookup(".scroll-bar");
            horizontalScrollBar.setBackground(new Background(new BackgroundFill(Color.rgb(12,40,60), new CornerRadii(0), new Insets(0))));
            // :horizontal无效
            ScrollBar horizontalScrollBar = (ScrollBar)scrollPane.lookup(".scroll-bar:horizontal");
            horizontalScrollBar.setBackground(new Background(new BackgroundFill(Color.rgb(12,40,60), new CornerRadii(0), new Insets(0))));
            // :vertical无效
            ScrollBar verticalScrollBar = (ScrollBar)scrollPane.lookup(".scroll-bar:vertical");
            verticalScrollBar.setBackground(new Background(new BackgroundFill(Color.rgb(12,40,60), new CornerRadii(0), new Insets(0))));
        });*/
        Rectangle rectangle = new Rectangle(600, 600);
        // 堆栈面板能展示全部的相对布局，-100和-200无效
        rectangle.setLayoutX(-100);
        rectangle.setLayoutY(-200);
        rectangle.setStroke(Color.BLUE);
        rectangle.setFill(Color.BLUE);
        stackPane.getChildren().add(rectangle);
        scrollPane.setContent(stackPane);
        primaryStage.setScene(new Scene(scrollPane));
        primaryStage.show();
    }
}

// 滚动区背景色
.scroll-bar {
    -fx-background-color:black;
}

// 无效，待解决
.scroll-bar:vertical .top-button {
    -fx-color:rgba(0,0,0,1);
}

// 纵向滚动块
.scroll-bar:vertical .thumb {
    -fx-background-color:
        #334db3,
        linear-gradient(to right, derive( #334db3,95%), derive( #334db3,10%)),
        linear-gradient(to right, derive( #334db3,38%), derive(#334db3,-16%));
    -fx-background-insets: 0, 1, 2;
    -fx-background-radius: 0.5em;
}

// 纵向滚动轨道
.scroll-bar:vertical .track {
   -fx-background-color:rgba(12,40,60,1);
}

// 横向滚动块
.scroll-bar:horizontal .thumb {
    -fx-background-color:
        #334db3,
        linear-gradient(to right, derive( #334db3,95%), derive( #334db3,10%)),
        linear-gradient(to right, derive( #334db3,38%), derive(#334db3,-16%));
    -fx-background-insets: 0, 1, 2;
    -fx-background-radius: 0.5em;
}

// 横向轨道
.scroll-bar:horizontal .track {
   -fx-background-color:rgba(12,40,60,1);
}

// 内容区
.viewport {
    -fx-background-color:rgba(12,40,60,1);
}

// 滚动条交叉角落
.corner  {
    -fx-background-color:rgba(12,40,60,1);
}

可参考官方文档：https://docs.oracle.com/javase/8/javafx/api/javafx/scene/doc-files/cssref.html#scrollpane