Earlier quoted context omitted.
then use kineto[1] or similar to cross-host your gemtext content as html over https, with your own css. 1: https://sr.ht/~sircmpwn/kineto/ (i do this for my blog, anachronauts.club/~voidstar. i kind of hate gemini-the-protocol, but love gemtext-as-default and love having a space where text-forward content reigns.)
But is there "Gemini over HTTP"? You can serve text/gemini files also HTTP(S), and also local files too. (On my computer I have it set up that it is capable of loading files of this format (locally and remotely), although most other programs are not capable of understanding this format)
ideally we'll tweak our gemini-to-http proxy to look at the client's "Accept:" header (as suggested in other comments on the op) to decide whether to reply with raw gemtext or converted html-with-css. then a www browser receives light formatting, curl receives raw gemtext, and gemini browsers format however they like.