Adding an external stylesheet to a Static FBML Facebook page is easy. You use the same code as you would with any other HTML page with a Link tag with a link to a URL like:

http://yourdomain.com/fbml.css

Great but you will soon find out after you make a change in your css after your first save that your changes are not showing up. This is a pretty fix but is not very obvious.

http://yourdomain.com/fbml.css?v=1

Facebook is caching your stylesheet so what you need to do is add some sort of change to your stylesheet’s URL so Facebook is forced to recache your CSS. Any type of query string variable attached to the URL like ?v=1 above will work.