if the interviewer is truly knowledgeable they can drill down into certain areas, or ask questions about the areas that weren't covered in the answer. i.e. if the answer was mainly browser DOM dynamics, ask about DNS and tcp/ip routing.

of course, the whole point of the question is nobody you're likely to interview can fully answer it. maybe someone like jim keller could but is someone like him really going to know about css stuff? maybe, maybe not.