You'll be able to add custom themes pretty soon. Hopefully within the next couple of weeks.
There's no fallback to the ANSI theme of the terminal as it breaks a lot of Textual's features.
There is a PR open at the moment relating to detecting the terminal background colour I believe, so in the future we could probably use that to choose a reasonable fallback.
I'm going to explore integration with other formats in the future. Right now there's experimental (incomplete) support for importing from OpenAPI v3. I'd like to add Postman and Insomnia collection importing too. Some kind of integration with Hurl could be very nice too, but would likely come further down the line.
I had a look at the Bruno website for the first time a few weeks ago, although I haven't tried it for myself yet. I'm definitely inspired by and agree with a lot of the principles behind Bruno: local first, developer friendly, readable/Git-friendly collections and so on.
I think I share a lot of the same motivations as Bruno's creator - I feel the landscape of HTTP API testing clients may actually have regressed in recent years from a developer's perspective, as the companies behind Postman/Insomnia etc. figure out how to monetise them.
What's the point of this comment other than being snarky/attempting to show off? You should reflect on it, because this would be a better place if people like you just didn't bother replying.
Maybe you don't find it valuable because your setup and mad vi skills offer you an alternative (which I'm very sure is just as feature-rich as what is described in the post, which you didn't read). Isn't it obvious how a more accessible solution might be useful to some people?
I for one welcome the efforts of the Warp team to improve terminal UX.