Had to specify Min width for it to work correctly.
Should width itself work, though? possibly bug?
Not a bug that is how Godot works. It is part of it’s upside down design.
The containers are in-charge of the size of each child. A child can only control it’s own size if you make your own UI scripts for it.
If you wonder what it looks like in practice, here is a file manager I made for my game:
It’s containers in containers in containers in containers…
It is messy to work with especially when searching for a script. There is no arguing with the developers over it; because it works, it is fast and even the memory footprint is small.