Wouldn’t it make more sense to just require the theme to include the CSS? Using a separate stylesheet for this seems kinda pointless when the theme can presumably be styled to cope.

There was a trac ticket regarding this back in 2.5, but I’m guessing was ignored.

We should probably lobby to have this fixed in core as the current system produces some bizarro code. I don’t understand why a definition list would be used in this way for a gallery. Each line is no different from the next, so an unordered list or table seems far more sensible to me.