I've read some posts today about how the deprecated "classic" theme can cause issues. I started with the classic theme on a particular database about 4 years ago. I immediately started changing styles and chose "Save as New Theme".
Years later, I doubt I use a single style from the classic theme, though a few of the default styles (which I don't use) still have the classic appearance. Does someone in my position need to be concerned about issues relating to the classic theme?