animation - Sliding Hidden Node -

i have question.

my question

how make rectangle hide under button when slides. not want come out of other side of button.

package javafxapplication24;  import javafx.animation.translatetransition; import javafx.application.application; import javafx.event.actionevent; import javafx.event.eventhandler; import javafx.fxml.fxmlloader; import javafx.geometry.pos; import javafx.scene.group; import javafx.scene.parent; import javafx.scene.scene; import javafx.scene.control.button; import javafx.scene.layout.borderpane; import javafx.scene.layout.flowpane; import javafx.scene.layout.gridpane; import javafx.scene.paint.color; import javafx.scene.shape.rectangle; import javafx.stage.stage; import javafx.util.duration;  /**  *  * @author phili_000  */ public class javafxapplication24 extends application {     public    button by;      @override     public void start(stage stage) throws exception {    flowpane root = new flowpane( );   root.setalignment(pos.center);   button butt = new button("play");   rectangle rect = new rectangle(200,40);       rect.setfill(color.violet);    translatetransition transition = new translatetransition(duration.millis(6000),rect);         scene scene = new scene(root,700,700);          transition.settox(-300);          root.getchildren().addall(butt,rect);        butt.setonaction((event) -> {    transition.play(); });         stage.setscene(scene);         stage.show();     }       public static void main(string[] args) {         launch(args);     }  } 

i tried best explaining, if have questions. or comment on how can improve questions. please, don't hesitate click 'add comment' button , give me ideas.

add rectangle first, button:

root.getchildren().addall(text, butt);