Border around all thumbs and pictures

Hi!
My gallery is almost finished ... i have just one wish left:
I would like to have a border around the thumbs and pictures, but i don't find the part in the CSS file where i can have something like that. I tried the border module but thats not what i wanted (just black simple borders..). I just want a simple white border ...
can someone help me to finish? i didn't find something here in the forum, too ...
greetz
quiri