Fluid header with fixed body

[jojojijijojo1]

Hello everyone,
I have a basic question regarding some css on vbulletin,
What I would like to do is to make the header fluid but keep the forum body fixed, an exemple of what I want to do is here http://vb4demo.skinden.com/forum.php?styleid=10 , as you can see the header is not aligned with the body, I know this may be basic, but I'm totally new to CSS.
Thanks for taking the time to read my question :)

[jojojijijojo1]

Any help? I have been searching around, and couldn't get it working, I know I need to remove the header from the body tag, but I have no idea how to it, any little help will be appreciated.

[AndrewSimm]

any help on this?

[Angle4cor]

I have the same problem and also cant find the solution for this...