Yes, you can. To do this, go to Settings → Notifications → Form User Options. Tick Send a confirmation message to the sender (autoresponder) and set up your settings. Press Customize to open the autoresponders lightbox if you want to edit a custom autoresponder or create a new one.
Select the Plain text radio button, right of Send email as, to enter the HTML mode and start typing your HTML tags and CSS properties and values. Use the HTML radio button to view the result.
If you are using another version of our notifications section, check out this article with the same subject.