Sidebar image caption – alignment, margin and padding?

I posted this elsewhere but now realize the css topic was probably the wrong place.

I’ve noticed that anytime I put a caption in the sidebar under an image, the text seems to default to a really large padding area to the right, like this.

Where in the css (or otherwise) do I find the code to modify in my child theme (based on twenty eleven) to change the caption margin, padding, and justification values?

Thanks

http://ww.wp.xz.cn/extend/plugins/image-widget/