Gmail has added themes! They are starting to send over the themes across all the servers. You can see if you have themes on your account by going to “Settings” and check if you have tab for “Themes”. You may need to change your Gmail settings back to old version, then go back to new again for them to show up. (At least I had to) If so, you should get a message asking you about changing your theme. Right now, I have the pebbles one installed — screenshot below.