Hi there,
i assume you mean in GenerateBlocks ?
When you add a Container Block to the top level of the page, in the Blocks Toolbar there is an option to Add Inner Container. The first time you do this, it gives you a tooltip to explain:

This will automatically add an Inner Container Block for you, and that inner container will have:
1. Sizing -> Max Width set for you to the Global width.
2. Spacing -> Margin Left & Margin Right set to auto which will center it for you.
We now give users a choice to add the Container only where they need it.