The admin settings page reads:
"Virtually every aspect of each theme is customizable with CSS. Themes are located here: /wp-content/plugins/photo-galleria/themes/."
The key here is virtually. When you get to edit the CSS you have to face a ton (way too much) of JS generated inline CSS. No use trying to control through stylesheet, as the same class and selector is shared by a lot of elements, so you screw everything up all the time.
Should I get into the code and add my custom classes so I can control them? Mmmmhh, that sounds like too much work, I will go for another plugin. But thanks for developing! I loved the lightweight aspect of it.