When you're using the ProtonMail app, you'll need to enter the code provided in the email. If you're using a Windows PC, you'll need to install the ProtonMail application on your desktop or mobile device. You can choose between six themes, including a dark theme. Then, you can customise your email messages by customising your account. There are many more features to choose from.
Read also - https://emailsdesk.com/protonmail-com-login/