Is it possible to have a fluid box, like the following:

This is just a bunch of text to fill space.
              ----------------

where "-" = a border centered and 75% the width of the div it is a part of.
The problem is that I can't use things like border, margin, or padding widths because they need to be in percentages and ie doesn't like that. The only thing that I can think of is to create a separate div just for the border.

I may post the actual (code) situation this is dealing with later if I need to.