I noticed few Foundation Class such as "menu-centered", "centered", "align-center" and probably few more classes is not included in elements foundation classes, is it because of RFF has feature of flex-box or we can use flex box instead?

It appears that the menu-centered is missing from the list only but you can manually type that class name in and it will work. This will be addressed in a future release.

As to the others, what Foundation offers now are the class names: small-centered, medium-centered and large-centered. These works on a per breakpoint bases.

Thank you .