> Yes, that seems like a good idea.  Something like this?  I also added
> another face for non-file-backed buffers, which helps distinguish
> them.

The attached patch fixes a bug with an anonymous face in the previous
patch.

By the way, it seems that, because the face `tab-line' inherits from the
face `variable-pitch', an anonymous face that inherits from
`tab-line-tab-special' (which defaults to italic slant in this patch) is
prevented from having italic slant applied.  If I set `tab-line' to not
inherit from `variable-pitch', the italic slant is inherited.
`variable-pitch' has not been customized, so it has no value for the
slant attribute, so it seems like it shouldn't interfere.  I don't know
if this is a bug in my code, in Emacs 28, or in the native-comp branch
that I'm using to develop this patch.

Thanks.