Wordpress Themes - WP Forum at BFA - I can't change the menu icons (eventhough I modified the css files)

Hello to everyone.
First of all, please apologize my poor english. I am not a native english speaker and I find it really difficult to read and understand what I find on the web.
I'm very enthusiastic about Montezuma. Unfortunately I can't manage to change the menu icons.
The url (a test, not consistent) :
www.woirgard.fr/blog
My main menu is made of three categories (id : 3, 7 & 4).
As I would like to have new icons instead of the star, I edit this from the "Using Menu Icons" section :

HTML Code:

/* Part 1- for default state: */

#menu1 .cat-?cat=3 > a > i { background-position: 0px -1944px; }

#menu1 .cat-?cat=7 > a > i { background-position: 0px -2352px; }

#menu1 .cat-?cat=4 > a > i { background-position: 0px -1728px; }

/* Part 2 - for hover state: */

#menu1 .cat-?cat=3:hover > a > i, #menu1 .cat-?cat=3.active > a > i { background-position: -24px -2184px; }

#menu1 .cat-?cat=7:hover > a > i, #menu1 .cat-?cat=7.active > a > i { background-position: -24px -2328px; }

#menu1 .cat-?cat=4:hover > a > i, #menu1 .cat-?cat=4.active > a > i { background-position: -24px -1752px; }

I copied this piece of code and pasted it within the menus_menu1.css file.
I did not replace any part of previously existing code, I added these lines of code.
I saved and had a look at my "new" site, but nothing changed.
Still this star, regardless which browser I'm using (Chrome, Firefox, IE)
I don't have a good standard in coding PHP and CSS, I certainly did something wrong...
But I can't see where...

Thanks in advance for your help.

toolaba