"Atom is slow and chromium a resource hog..."
Check Sciter (http://sciter.com) then. It is single dll/so/dylib of 4-8mb without any external dependencies.
On Windows Sciter uses Direct2D that is native H/W accelerated graphics rendering layer. Yet it allows to render UI directly into DirectX surface : http://sciter.com/sciter-and-directx/
> We have no intention to cover full CSS1/CSS2 attibute map.
Yeah that's not gonna work out for many projects.