You did not include the .artx file in the zip you sent so I cannot see what it looks like in Artisteer. But I can see the exported index.html file and it does not have a center aligned menu, so I don't think it is center aligned in the Artisteer design. It is left aligned in the design from what I can see. If the design in Artisteer was center aligned I could probably fix it in the skin (or it may not even need fixing), but at this point I conclude it is not center aligned in the Artisteer file. If you send the .artx I will check again.