[LorenDB]

ChatGPT is not capable of reworking site-level CSS. If it were, that would probably be classified as a security vulnerability. Your best bet is to complain to OpenAI or (if you are throwing money at a premium subscription) find a third-party client to use that has theming that you like.

[harborsong]

It wouldn't be a vulnerability if we can request it to show its output in a legible theme, none that I can see, what am I missing?

[LorenDB]

What you're asking for potentially involves ChatGPT to be able to arbitrarily manipulate page-level CSS, which could in theory be exploited for nefarious purposes, maybe by a system prompt from the ChatGPT store.