What do you think... would this second approach be more robust if future changes to classes are made?

Yes, you're right, it is today difficult to always maintain a custom theme pack for a good reason : i'm improving it!

But, i try to give important infos here (and will update it as soon as possible) : www.icagenda.com/docs/documentation/13-t...e/theme-pack-upgrade

About the new class naming, with the .ic- prefix, they won't changed as a name, but could of could change due to code enhancement.

The most advanced theme is today "default", and i have still a work to do with ic_rounded. In fact, this was due to none standard coding before, and now i have much more skill and knowledge, i'm little by little improving the code to give the best one as possible!

So, if you don't have to change the structure, use an override of css class in your main site template css file.

Having a custom theme pack is only needed when you want to change the html structure

Hope this help!
Regards,
Cyril