Great question! I'm still experimenting with how responsive layouts should work, but so far: small/simple components like "Button" aren't responsive, while more complex components like "Hero" have responsiveness built-in.

At the css level, "top-level" components are absolute positioned, but nested components are layed out with flexbox.

There's no way to bring your own React component library yet, but once that's possible, you can always make things responsive in the library itself too.

> At the css level, "top-level" components are absolute positioned

I’m not the target for this kind of tool, so please take this as a soft critique if any at all: everything up to this point has struck me as positive, but this registered a big “yikes!” in me. I’d think top level components would be by far the simplest to handle reflow without any specific positioning considerations.

Feels like you’ll need to be leveraging something like container queries in order to make smaller components responsive.

I agree, container queries feel like a natural fit. I saw that they're supported in every major browser now, but haven't personally tried em yet.