Editing twitter style on twitter-widget-pro plugin using wordpress



I’m running wordpress and have downloaded the twitter-widget-pro plugin. I’m trying to customize the appearance of the tweets to suit my website and have tried to copy and paste some custom styling into the style.css file as well as uploading the sprite png. However when I refresh my page it doesn’t actually make any changes to the Twitter output.
I think my custom theme may be over-riding the changes to the widget, any idea how to fix this?
My site can be viewed at http://cornwallbingo.co.uk, its running the Karma wordpress theme.

Thanks for any help!