[Spoom]

Agreed with siblings stating that the question is arcane, Googleable best practices knowledge. Any time I want to find the answer to something like this, I Google it.

The author should ask themselves honestly if they ask this question just so they can quickly say, "Nope, wrong! Your answer doesn't cover [X number of unstated assumptions]." While I understand things are complex, my first answer would have been something along the lines of position: fixed; bottom: 0;. If that makes me wrong because it doesn't work on [Y smartphone] or [Z tablet], then two things need to be done to make this question worthwhile:

1. State your assumptions and intended audience up-front.

2. Allow the candidate to Google.

If the candidate is allowed to research and put together a comprehensive answer based on the knowledge they've gathered, that turns this question into a much more insightful one.