Styles won't delete from Styles and Formatting

[RoboHelpHelpNeeded]

I'm using Robohelp 19 Classic. I have a bunch of styles that show up in the Styles and Formatting pane that do not appear in my .css file and based on a text search of the html files also do not appear to be used in any project files. When I right-click and choose Delete, I get a prompt asking me if I'm sure I want to delete. I say Yes. And the style remains. Since it's not in the .css file I can't delete it directly from there. How can I delete these unused styles? 

[Amebr]

Which styles? There are a few that are RH specific and will show up even when you don't have a stylesheet applied to a topic, for example "breadcrumbs". Given they show up even without a stylesheet, I imagine they can't be deleted.

For example, here's a topic without a stylesheet, and a sample of a couple of the styles that show up anyway.