Hey, just to let anyone who’s interested know – I made this default theme template in Sketch after all since I need it for my own design customisation. Feel free to reuse it – I uploaded the files to GitHub:
So far it’s only the topic list screen on desktop and mobile views, but I think that this gives you a good starter for experimenting with your own theme. Later on it would be nice to also have a topic view too.
I also created a screencast while I was making this template (narration in Croatian) in case anyone finds that helpful: