Can someone explain how this container works? The examples render properly all right, but it's as if the code running in the back wasn't what's advertised in the examples' source.

I'm trying to use this as my root widget, and nothing gets sized appropriately and no I don't want to have to do width=100% on every single child in there and quite frankly it doesn't seem to work either.

How do I get that container to take 100% of the screen?

Thank you.