Ok, one small victory today. Finally figured out how to write user-styles in Nyxt. I'm not comfortable with OO style nor the Nyxt codebase but slime-doc-contribs, macroexpanding, and inspecting slots in slime helped a lot. Coming from Emacs, I definitely miss that level of built-in documentation I expect from an extensible environment but the Nyxt codebase does have good documentation strings of the important bits. Could be better with examples but I can get by.
Now, because its all nice CL, I can move forward and get rid of writing CSS in strings myself, and instead write it in a Lispy way using Shinmera's LASS library. But one step at a time.