CSS Positioning questions

Hello!
I've been trying to solve a CSS problem for too many hours, so now I'm calling out for help.

I'm designing a site at Home. It is a Joomla 3.x installation using your YouSimpleGrids template. I've mostly been modifying the 'blue.css'.

There are two issues I just can't find the solution to. First , the transparent gray background should be 100% of the width. It works in the header and footer but not in the body. I've tried changing <div id="centerbottom" class="yjsgsitew"> to a width of 100%, but then everything floats left. Can someone help me with the CSS for that?

Second, the header, body and footer blocks should have a vertical offset that is a percentage of the browser height. (The gray block needs to be at different heights on different pages and needs to always be at the same place on the background image, no matter how the browser is resized. The background image resizes with a 'supersize' PlugIn.) At the same time, the content block needs to stay centered horizontally. Can someone help me with the CSS for that?

This is how it ought to look:


I'm so thankful there are people out there who are much better at this kind of thing than I am!

Thanks for any help!
Larry

Are you sure your are posting in product assigned forum?: Yes

What is your CMS version?: WordPress 3.x

MySQL Version: 5.x

PHP version: 5.x

Link to installation: Home

Have you edited any files? If yes tell us which ones.: Yes

Is this personal or client website?: Client

Are you sure your are posting in product assigned forum?: Yes

What is your CMS version?: Joomla 3.x

MySQL Version: 5.x

PHP version: 5.x

Link to installation: Home

Have you edited any files? If yes tell us which ones.: Yes

Is this personal or client website?: Client

Sorry but team has no time for custom work , some of the customers might help.

Thanks Neo,
I know you are a busy man. You've helped me several times in the past. Perhaps someone can point me to the right DIV or CSS-style. I'll be happy to take it from there.
Larry