TestFX.java

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.StackPane;
import javafx.scene.layout.VBox;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class Test extends Application {
    Label getLabel (String text, int fontSize) {
        Label label = new Label(text);
        label.setStyle("-fx-font-size: " + fontSize + "px; -fx-text-fill: white;");
        return label;
    }

    Button getButton (String text) {
        Button button = new Button(text);
        button.setPrefSize(200, 50);
        button.setStyle("-fx-font-size: 18px;");
        return button;
    }

    public void start (Stage stage) {
        int w = 640, h = 480;

        StackPane root = new StackPane();
        root.setStyle("-fx-background-color: #000;");

        AnchorPane container = new AnchorPane();
        container.setMinSize(w, h);
        container.setMaxSize(w, h);
        container.setStyle("-fx-background-color: #29f;");
        root.getChildren().add(container);

        VBox hbox1 = new VBox(10, getLabel("RedSquareFX", 32), getLabel("Version 1.0", 18));
        AnchorPane.setTopAnchor(hbox1, 20d);
        AnchorPane.setLeftAnchor(hbox1, 20d);
        container.getChildren().add(hbox1);

        VBox hbox2 = new VBox(10, getButton("Play"), getButton("High Score"), getButton("Settings"), getButton("Help"), getButton("Credits"));
        AnchorPane.setTopAnchor(hbox2, 20d);
        AnchorPane.setRightAnchor(hbox2, 20d);
        container.getChildren().add(hbox2);

        VBox hbox3 = new VBox(10, getLabel("Made by Bastiaan van der Plaat", 18));
        AnchorPane.setLeftAnchor(hbox3, 20d);
        AnchorPane.setBottomAnchor(hbox3, 20d);
        container.getChildren().add(hbox3);

        VBox hbox4 = new VBox(10, getButton("Exit"));
        AnchorPane.setRightAnchor(hbox4, 20d);
        AnchorPane.setBottomAnchor(hbox4, 20d);
        container.getChildren().add(hbox4);

        stage.setTitle("RedSquareFX");

        Scene scene = new Scene(root, w, h);
        stage.setScene(scene);

        ChangeListener<Number> stageSizeListener = (observable, oldValue, newValue) -> {
            System.out.println(scene.getWidth() + "x" + scene.getHeight());
            double scale = scene.getWidth() < w * scene.getHeight() / h ? scene.getWidth() / w : scene.getHeight() / h;
            container.setScaleX(scale);
            container.setScaleY(scale);
        };
        stage.widthProperty().addListener(stageSizeListener);
        stage.heightProperty().addListener(stageSizeListener); 

        stage.show();
    }
}