After viewing the move to "containers" for custom corners themes, I've tried to rework the contrib wood_custom_corners theme to use the new containers.
And I've found that, in some situations, where the number of "containers" in a page is high, it's really difficult to point to CSS selectors properly, because nothing differences one container within another container within another container.... from his parent (or at least if forces to write really LONG CSS selectors to match the desired container.
So I've thought about to add one new "wraplevelXX" (XX = level or depth of the container) class to each container, in order to be able to select them easily with CSS.
I think it isn't dangerous (nor heavy) at all because only adds one new class to each container in a page. And it really provides high control about what to do with each container level.
Patch attached. +1 to add this. It can help future custom corner themes for sure (at least the woody one will be benefited).