You can now view the html code for your emails, and edit as you see fit.
This is for advanced users who know about html.
Inside the email editor, go to the rightmost icon (HTML) and click on that to switch to html mode:
Once you're done viewing/editing the html, click the icon one more time to switch to the normal visual mode.
Please don't go overboard with the styling/design of your emails as it impacts your email deliverability. This is one of the major reasons why we don't natively build fancy-designed email templates into the system. We use a simple email template to keep the backend html code as clean as possible, which email inbox providers like.
Also, we believe that as content creators, you should focus in creating GREAT CONTENT rather than worrying about fancy-designed emails. After all, your contacts subscribed to you in the first place because they expect your content to be great, not because they expect your emails to have fancy design.