Custom CSS in NextGen Gallery

I want to have a custom css for the single images that are drawn into a blog post with the nextgen shortcode - so that I have my own custom 'mode' that produces a border around the image.

[ singlepic id=x h=height w=weight mode=web20 ]

http://nextgen-gallery.com/singlepic/

more css details here
http://nextgen-gallery.com/templates/

Example css
http://webdesignerwall.com/tutorials/css-decorative-gallery

Please create something like 6. Grungy Watercolor so it works smoothly on various sized single images.