Adding shadow to navigation bar

I want to add shadow to the navigation bar like this one:



I want to do it using Gimp or regular CSS

 

CSS

http://css-tricks.com/snippets/css/css-box-shadow/

Code (markup):

GIMP

http://gimp.linkvier.com/2012/08/how-to-add-shadow-in-gimp.html

Code (markup):

 

Shadow like that only in an image; in CSS, box-shadow look only like this:
You can put a background image like this:

 

shadow is not created by css or any other script this is image.