Add RemoveChild to IParentableElement, only resize Container if children overflow it.

TestGame/TestGame.cs

@@ -73,9 +73,16 @@ public class TestGame : Game
             _container.AddChild(new RectangleWidget(new Rect(32.0f, 32.0f), MathUtils.RandomColor()));
         }
 
+        if (Input.IsActionPressed("cancel") && _container.Children.Count != 0)
+        {
+            var lastChild = _container.Children.Last();
+            _container.RemoveChild(lastChild);
+        }
+
         if (Input.IsMouseButtonDown(MouseButton.Left))
         {
-            _particleSystem.SetEmitterPosition(_emitterId, Input.GetMousePosition());
+            var mousePos = Input.GetMousePosition();
+            _container.Size = new Rect(mousePos.X, mousePos.Y);
         }
     }
 
@@ -118,5 +125,5 @@ public class TestGame : Game
     private ResourceRef<Sound> _sound;
     private ResourceRef<Texture2d> _icon;
 
-    private GridContainer _container = new();
+    private GridContainer _container = new(minimumSize: new Rect(64.0f, 64.0f), new());
 }