[Cleaner Gallery] / WP gallery shortcode: how to style gallery?

Hey guys,

I’m still pretty new to WordPress and have run into a problem using the [gallery] shortcode. I am using the “Cleaner Gallery” plugin for most of my galleries on http://www.knowingme.org, some of which you can see on the front page (e.g. in “Laura: The Red Side“).

You can see that the empty space in the middle between the images is pretty big, especially when compared to the margin above and below. I’d like it to be smaller, but I don’t know in which CSS style sheet this gallery is styled, and which elements to style.

Can you help me out?

Thanks!
M.