[Plugin: NexGen Gallery] Add solid border around thumbnails

I would like to add a solid black border around each of my thumbnails. I tried changing the coding in the css (style) file but it didn’t do anything. Any suggestions would be great. My site isn’t live yet so it’s okay if you have an idea that you’re not sure will work.

Here is how it looks now: http://66.147.244.166/~craftyhi/blogger-portfoilo/

Thanks y’all!