Simple Question – Centering the Thumbnails in a Post Slider

Hi Folks;
What I wanted is pretty simple: I simply want to center the thumbnail images used in the Post Slider entries. Right now they are all left-justified. I will add that it’s sort of odd, since the default icon is centered (the one used when you don’t specify a featured image).
I’m sure it’s probably just a CSS tweak, but I can’t seem to pinpoint the right code, and figured someone could answer it quicker than I could chase it down..
Any help would be appreciated.
Thanks!