Here is a screenshot for "new reply notification email". It's simply a HTML message so you can use any design you like. It's just a sample I use in my board.
Notice that the screenshot is NOT a webpage! It's the EMAIL your members (who choose to recieve HTML mails) gets. It looks like a webpage because it's in HTML format

This also clarifies what "HTML email" mean if you dont know the term. In an other words HTML mails are the mails with color/background/images/bold-italic-underlined fonts just like web pages..