Apply this diff to HelloRectangle.java:

diff --git a/apps/toys/Hello/src/main/java/hello/HelloRectangle.java b/apps/toys/Hello/src/main/java/hello/HelloRectangle.java
--- a/apps/toys/Hello/src/main/java/hello/HelloRectangle.java
+++ b/apps/toys/Hello/src/main/java/hello/HelloRectangle.java
@@ -31,6 +31,7 @@
 import javafx.scene.paint.Color;
 import javafx.scene.shape.Rectangle;
 import javafx.stage.Stage;
+import javafx.stage.StageStyle;
 
 public class HelloRectangle extends Application {
 
@@ -51,6 +52,7 @@
 
         root.getChildren().add(rect);
         stage.setScene(scene);
+ stage.initStyle(StageStyle.UTILITY);
         stage.show();
     }