Question about adding css to email confirmation

On the notifications screen for your form, you can Disable Auto-formatting; with a check box beneath the Notification Message (bottom box on the screen.)

Once that's turned off, you have complete control over the body of your email message. You will have to use simple inline CSS since not all email clients handle CSS gracefully. You'll have to build the body of the email yourself using the drop-down to insert form fields, but then you can wrap that data in whatever CSS you want.

Here are a couple screenshots of the user notification, one with default formatting and {all_fields} another with just a couple fields and some inline HTML and CSS.
http://min.us/mvnE53p

Here is the body of the notification I used (just to show how it was done for a couple form fields.)
http://pastie.org/2156403