:beetle: Prevent Godot to have a white tooth

godot/slides/204/PhysicsEngine.tscn

@@ -11,6 +11,7 @@ viewport_path = NodePath("SubViewport")
 script = ExtResource("1_ag2av")
 
 [node name="SubViewport" type="SubViewport" parent="."]
+transparent_bg = true
 size = Vector2i(1920, 1080)
 
 [node name="Demo" parent="SubViewport" instance=ExtResource("2_u43ho")]