Add classes in new Container Layout Panel

I just discovered the Container Layout Panel to create multiple Inner Containers, when adding a new container by clicking on image .
It took me a while to find the settings of the margins and paddings of the inner containers - so I found it at Layout > Inner Container of the parent container.
I wished to have the possibility to add classes to the inner containers when creating a new “flexbox grid”. Because we can’t use multi selection of elements, yet, I would be a very nice to have to not adding classes to each single inner container.
Prove me wrong, maybe there is a option and and I can’t find it.