Got the drag thingto work

src/sample/Main.java

@@ -1,15 +1,19 @@
 package sample;
 
 import javafx.application.Application;
+import javafx.event.EventHandler;
 import javafx.fxml.FXMLLoader;
-import javafx.scene.Node;
 import javafx.scene.Parent;
 import javafx.scene.Scene;
+import javafx.scene.input.MouseEvent;
 import javafx.stage.Stage;
 import javafx.stage.StageStyle;
 
 public class Main extends Application {
 
+    private double xOffset = 0;
+    private double yOffset = 0;
+
     volatile double[] posOrigin = {0, 0};
 
     @Override
@@ -26,8 +30,19 @@ public class Main extends Application {
         root.lookup("#exit").setOnMouseClicked(event -> primaryStage.close());
 
         // Drag
-        root.lookup("#rectangle").setOnMouseDragged(event -> {
-
+        root.lookup("#rectangle").setOnMousePressed(new EventHandler<MouseEvent>() {
+            @Override
+            public void handle(MouseEvent event) {
+                xOffset = event.getSceneX();
+                yOffset = event.getSceneY();
+            }
+        });
+        root.lookup("#rectangle").setOnMouseDragged(new EventHandler<MouseEvent>() {
+            @Override
+            public void handle(MouseEvent event) {
+                primaryStage.setX(event.getScreenX() - xOffset);
+                primaryStage.setY(event.getScreenY() - yOffset);
+            }
         });
 
     }