ContentFrame.java

import javafx.geometry.Pos;
import javafx.scene.Node;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;

public class ContentFrame extends StackPane {

	public ContentFrame(Node content) {
        setAlignment(Pos.CENTER);

        Rectangle frame = new Rectangle(200, 200);
        frame.setArcWidth(25);
        frame.setArcHeight(25);
        frame.setStroke(Color.WHITESMOKE);

        getChildren().addAll(frame, content);
    }
}