Update: This article refers to the 1.0 version of ProtonMail so this article is now outdated.. Themes in ProtonMail are being revamped, so stay tuned for updates regarding themes in ProtonMail 3.0.
We’ve added built in themes so you can customize your ProtonMail experience with themes made by our team and our world-wide community. The other exciting news is that we are now approaching the ProtonMail 2.0 release which will contain some major enhancements. We are also happy to report that our iOS app has now been submitted for App Store approval!
To find our new themes, go to the Settings page and then click on the Themes tab.
ProtonMail currently supports 4 themes, including a dark green theme from ProtonMail user _csalmeida.
Anyone can submit a theme if you know CSS at our official Theme Tumblr page here: http://protonmail.tumblr.com/
Note that themes are still an experimental feature and only the default theme is supported 100%. Custom themes might not work on all browser and all operating systems and platforms (like mobile and tablet).
Stay tuned for more updates!