Background layout problem when using dropdown menu

[#1]

Hi there!

I'm trying to use Petra Bloem's great dropdown menu extension but, when using it in the Ajax server environment in IE9 and up, the document's background drops to the bottom of the screen.

That does not happen in the web view or in IE8 for example.

My guess is that I need to change something in the CSS file, but have no idea what.

Can anyone help?

I'm enclosing a screen shot (the banner should be on top) and the CSS file of the extension.

Thanks!

Ajax:

Webview:

[#2]

Anyone??