To reproduce decrease the width by slider at the top

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.Scene;
import javafx.scene.chart.PieChart;
import javafx.scene.control.Slider;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;

public class JavaCharts extends Application {

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

    @Override
    public void start(Stage stage) throws Exception {
        ObservableList<PieChart.Data> data;
        data = FXCollections.<PieChart.Data>observableArrayList();
        for (int i = 0; i < 10; i++) {
            data.add(new PieChart.Data("Data item " + i, i * 100));
        }
        PieChart chart = new PieChart(data);
        chart.setTitle("PieChart");
        chart.setStyle("-fx-border-color: darkgray;");
        chart.setPrefSize(300, 600);

        Pane pane = new Pane();
        pane.getChildren().add(chart);
        
        Slider slider = new Slider(0, 300, 300);
        slider.setShowTickLabels(true);
        slider.setShowTickMarks(true);
        slider.valueProperty().bindBidirectional(chart.prefWidthProperty());
        pane.getChildren().add(slider);
        
        pane.setPrefSize(600, 600);
        Scene scene = new Scene(pane, 700, 700);
        stage.setScene(scene);
        stage.show();
    }
}