Center Thumbnails

Hi there,

I want to use “thumbnails only” – how to center the thumbnail?

Tried this in css, but it didn’t work:

.srp-widget-thmb {
margin:auto;
}

and

.srp-widget-thmb {
align: center;
}

Thank you!

http://ww.wp.xz.cn/extend/plugins/special-recent-posts/