positioning question

layout design: liquid, with header, left floated menu, and main content

What css rules should I apply to get the blue header appear behind the left orange menu? I know that a neagtive margin is required to get the header to drop below the top of the menu, but I do not know how to get the blue header bar appear BEHIND the menu.

Here is an example site, just to shouw the idea; the header in blue behind the left orange menu bar: http://www.zorginbeeld.be/

And here is what I made of it so far: http://mysafety.be/zorginbeeld.html

positioning question

Erik Arckens wrote:

but I do not know how to get the blue header bar appear BEHIND the menupositioning question

Sure, thanks. Could you maybe give me a hint on html and css coding please?