How can I set a Node2D or a Control to show behind the root viewport? I have some items that I only want to display if there's nothing shown in the root viewport at that location. I already know to do
get_viewport().transparent_bg=true, but for the life of me I can't figure out how to use Node2D's z-indices or Control's show behind or show on top features to get them to display behind the root viewport.
How do skyboxes do it, for example?