Is it possible to change the main menu style using custom.css ?
@TE I am planning to use this one :http://cssmenumaker.com/menu/flat-jquery-responsive-menu
nope, not possible via custom.css..
that menu is not just CSS, there's also a javascript file and you need to modify that code or the html structure in GenericMenu.template.php
Which are the affected files then ? Only custom.css and GenericMenu.template.php ?
nope, the menu has got a script.js file.. extract that file and you'll see it:
http://cssmenumaker.com/sites/default/files/menu_source/361/source.zip