The 3.0 version of ProtonMail brought many changes, such as a new column layout to go along with the existing row layout. Many other changes, such as improved cryptography to support public/private key encryption with custom domains, are largely invisible to the user. Thus, the new look is the most noticeable change to the user experience.
Overall the new theme has been well received, but some people have written us to say that they prefer the original ProtonMail look. It is possible to switch the theme of your secure mailbox to the original theme by going to Settings –> Appearance and selecting “Load Classic Theme” at the bottom of the page. If you also set the inbox layout in Row mode, then ProtonMail 3.0 will look almost identical to ProtonMail 2.0.
The classic theme is favored by some because it has a higher contrast than the standard theme. If you feel the standard theme doesn’t have enough contrast, we recommend trying the Classic Theme. In the coming months, we will be releasing additional themes for ProtonMail, but if you can’t wait, it also possible to modify the CSS to build your own theme. We recommend doing this only if you know what you are doing however, as this could break your inbox if done improperly.
The ProtonMail Team