Styles management, what is the "runtime" category?

Spring cleaning here so I’m trying to clean up, rename, reorganize, my styles collection. Anyone know what the “runtime” category is for. That folder was deleted from the directory, and if selected that option is now empty, but the name is there after several restarts. It was a separate path for that folder stored in a different location than the others, wonder if that matters, but had been working until I deleted it. I don’t see a way to remove custom collections from within Sketchup.

I think the runtime category is the list of recent used styles, it took me several startups to get rid of. (3x)
With save (Saving untitled file)

That worked, I have no idea why, but saving an empty untitled file a few times in tandem with restarts cleared the list. Cheers @MikeWayzovski