No more boring and black login screens! Squarespace has just released an option which allows you to customize the login screen used for password protected pages (limit one page design for all login pages).
In my opinion, this is a much-needed addition to their feature set as you can now brand your login pages with your own logo, 
background images and fonts. There are currently 6 basic page styles to choose from. The interface and level of control is very much like the SquarespaceCover Page option (no blocks). To access the new Lock Screen customization option, go to the Design panel and look for “Lock Screen”.
For more information, check out their blog post announcing this new feature or this new Squarespace guide, Designing a Lock Screen.
