Could you please have a look at http://raufthecoder.wordpress.com/2011/08/06/per-site-customization-in-mozilla-firefox/ . It explains how to customize Mozilla Firefox using 'userContent.css'. How can I do it in Internet Explorer ?
Internet Options->General->Accessibility->Format documents using my style sheet :
In Internet Explorer (or the Control Panel), select
Now your user-stylesheet will be applied to all websites that you browse, depending on what you put it in.