Style MultiExcerpt Fast, MultiExcerpt Fast Include for legacy pages
The "Fast" Multexcerpt macros should be styled for legacy pages because the "Fast" macros are not needed in the new fabric pages.
The "Fast", a.k.a. dynamic, Multiexcerpt macros were introduced to workaround a problem with Atlassian rendering old legacy pages. Atlassian was blocking page render until all static macros were processed. The "Fast" macros are most helpful in legacy pages so they should be styled for legacy pages.
Because Atlassian does not provide a stylesheet for Connect apps, the dynamic macros cannot get it from the framework and must make a (hard-coded) decision about which style to use (legacy or new).