Tweaking the Dialog style

What is the best way to tweak a dialog's style? In my attached dialog, for example, I'd like to center the title and the button and put more vertical space between the input fields but it's not clear which of the hundreds of styles in my jquery-ui-1.8.1.custom.min.js controls each of these. I have the Firefox Web Developer plugin installed but it doesn't work for the jQuery dialogs.

Thanks for any suggestions.