Dan, the '+' simply says you have changed the base Style in some fashion.
Say you embolden one word in Normal, that would then show as Normal+. Ditto for a font size change.

Styles usually need to be larger in variants as the screen view is much smaller.

You can always unlink the text and then you can do what you like (without changing the Styles). That does require keeping two copies of the text aligned.
This is actually better in many cases as who wants to read War and Peace on a phone when you could just write (spoiler ahead - highlight between the quotes), 'They all died!'

Acorn