Custom navigation on top

Can anyone point me in the right direction in setting up a custom navigation system? I’m a newbie at css/html and I’m not sure how I can add custom buttons using the human condition style (3rd place in alexking’s competition). or any style for that matter. Agaain, these are custom buttons/links I’d like to insert aside from what’s in the menu in wordpress. Does anyone know where on the index.php/wp-layout.css I can insert this code?
Thanks.