I was responding to a post about design, so this reply was about design.

Yeah, it's a subjective opinion. Something looking good is also an opinion.

What I mean by non-functional is that the attempt at design was non-functional on my browser resulting in dead space and unattractive design.

Since this book is about programming, it already sets a precedent for potentially pretty but non-universally-working solutions. Something I personally try to avoid as much as possible.

Other issues with the design is huge unattractive margins and the main page containing almost no information when first loaded.

Honestly, this all wouldn't normally bother me as there are tons of books whose online sites have OK at best design. And maybe it's a great book, but complimenting it on design specifically seems wrong.