Something I did not expect: my HTML ebooks, and the site in general, look pretty darn good on my flip phone's browser. I think there's some potential to make it really solid. Even the dark mode worked well, which was a sight to see.
It felt really good to see this. I'd read a blog post somewhere that you want your website to be functional on a crummy PSP browser. Seeing everything work on a flip phone made me feel like I'm the right track for #accessibility.