The new location for both Section and Container defaults is: Global Styles → Elements → Blocks panel.
From the Release Notes for 1.2.9.8:
In addition, we are introducing block-specific styles in the Global Styles → Elements → Blocks panel. These styles will apply to the default block class, and you also have the option to target specific blocks by entering a class, similar to our HTML element styling.
Initially, you can find the Section and Container block styling options, with more to be added in future updates.
The full text of the Release Notes are - here.
Also check out Grant Ambrose’s video after which it will become very clear where the new default settings are located and how to set them:
Cwicly FIXED one of their biggest issues
Best of luck!