Very interesting. I cant find the #header div in the css. I see you are using it :
<div id=header> but i cant find it in the css. How do you control it?
Its not there in the default css. You can however add it and style it as you please since the div with the id is already there.
It wasn't, it wasn't needed to. Its a "container" for other divs that needed to be styled such as panel. I assume it was added to make it easier for themes to use it to style the header the way they want to. Same thing with the logo div.
Not every div needs to be styled.
You can style it yourself, simply add:
#header {
background: #values;
padding: #px;
margin: #px;
etc. etc. into the global.css