Weird nitpick. There are almost no GUI toolkits that run everywhere, including embedded systems (i.e. microcontrollers). The only one I know of is Slint.
It's not a nitpick to point out that the explicit claim of running everywhere is horseshit.
Doesn't run on my fridge? Liars.
Also <2mb doesn't really seem lightweight to me...
You can get down to less than 60k. It’s just the average binary that links in various system resources with no size optimizations comes out at around 1.5mb. Tiny for desktop!
For a web-based UI, if it manages to stay in the single-digit range I'd call that acceptable for all the functionality that you get in return. And I say this being skeptical of anything web-based in general.