The layout engine in gngr was designed in the CSS1 era. It was updated to support CSS2 during the conversion from Lobo Browser to gngr. However, it needs a whole new approach to support newer standards and to keep it maintainable.

I have been working on a prototype here:
https://github.com/LiMium/soda

... partly to improve my understanding and partly to use it as a playground for design ideas.

It is written in Scala to allow quick iterations. The plan is to eventually migrate to Java or Kotlin.