@betro-hakala I don't even know what you want to be transparent. Also, if you are using Vanilla theme (not Persona) then the theme's options won't be in NodeBB Category options, those are completely different.
Could you send a screenshot of what you want transparent? That would help us help you.
Obfuscating the email address does not raise the bar much as bot scrappers and ai will only continue to "progress".
So we're left with encoding. Thankfully, at this juncture at least, most scappers are either not onto this or don't care since since a fringe case? Whatever. Still no magic bullet. But maybe best of the low hanging fruit options since should be easy peasy to code.
Trying to mitigate email abuse is a noble goal. We just need to actually "game it out" cuz that is what this all boils down to for the AI hotshots. Else otherwise all you got is purely psychological protection...., a.k.a. PPP. Which is not a bad thing. If/when it's you're only thing. But.. just sayin.... stuff happens on the sharp end.