They just added "themes"... allowing you to select different templates to display your mail. I'm enjoying "shiny." Maybe you'd like "terminal."
ADDED: Apparently, this is being "rolled out" over the next few days, so you might not be able to do it yet. I noticed it was available when I was automatically switched to the new default. (It's possible to go back to the original look by choosing "classic.") I also had a message at the top of the page to click to the themes choices, so it was obvious what to do. You can try going into settings and seeing if you've got a "themes" tab. Good luck!