Do you have any filters setup for the plugin? (i changed some of the filter names today, apologies for that - so existing filters you have for the plugin will need updating).
I can see the CSS uri(the URL to the UI theme CSS) does not include a theme in the URL.
Viewing source on your page i can see this line.
<link rel='stylesheet' id='jquery-ui-tabs-css' href='http://ajax.googleapis.com/ajax/libs/jqueryui/1.10.2/themes/jquery-ui.css?ver=1.10.2' type='text/css' media='all' />
Which should something read along the lines of..
<link rel='stylesheet' id='jquery-ui-tabs-css' href='http://ajax.googleapis.com/ajax/libs/jqueryui/1.10.2/themes/THEMENAMEHERE/jquery-ui.css?ver=1.10.2' type='text/css' media='all' />
Bring the settings page up for the plugin and hit save, maybe the skin selection got lost some how(no idea why that would happen).
Let me know if that helps.
Whatever the cause, it's an easy fix once we can work out why it's not picking up a skin selection for you. :)