I am trying to have a better understanding of fluid layouts.

I read this article, which was really interesting: A List Apart: Articles: Fluid Grids

Here are a few quetsions:

1) What I don't understand about font sizes, is how you know in the first place the default numbers with which you're going to work. Do you have to assume all fonts will be 16px, and then work based on that fact?

2) Is there a way to impose a default font size to user agents?

3) When you set a #wrapper that is, say, 98% wide. 98% of what? Is there a number you set in the first place?

4) Is it possible to say that a #wrapper is 960px wide and still have a fluid layout?