I have just coded an email design, tested it in Litmus & found out the following errors:
Outlook.com: There was no background image for the newsletter & some of the headings (h4) font color is totally different. Although the same color is OK for the links. outlook 2003-2011 works fine.
Hotmail: Similar is the case for hotmail as it also doesn't show up the background for the newsletter.
Here are the litmus results.
https://tahir.litmus.com/tests/9401666/versions/2/screenshots
Here is the code for background image:
<body background="http://gallery.mailchimp.com/ab941597d81bf8a59e91efd1f/images/body_bg_.3.jpg" leftmargin="0" marginwidth="0" topmargin="0" marginheight="0" offset="0" style=" width:100%; margin: 0;padding: 0;width: 100% !important;-webkit-text-size-adjust: none; background-image: url('http://gallery.mailchimp.com/ab941597d81bf8a59e91efd1f/images/body_bg_.3.jpg'); background-repeat:repeat-y no-repeat; background-position: top center; background-color: #5c130a;">
<!--[if gte mso 9]>
<v:background fill="t">
<v:fill type="tile" src="http://gallery.mailchimp.com/ab941597d81bf8a59e91efd1f/images/body_bg_.3.jpg" />
</v:background>
<![endif]-->
Thanks.
Keep in mind, that CSS is not supported equally by the Clients (and Versions)
To get an overview you should take a look at http://www.campaignmonitor.com/css/