You're not on a paid account, so I don't know what you're doing with "custom CSS", however it sounds like you're making a directory?
Most directories have the instructions to make a completely empty folder and place the directory in it, then in your folder settings, make that your Default Folder. Alternatively, Protecting the folder doesn't private the characters but removes it from navigation and keeps the characters in that folder hidden from View All, though unlocked folders within it are not. I have four locked folders in my Unsorted, the first of which is a completely custom-coded "Sorted" folder which is also my landing page when hitting Character. Even if a folder is Protected, it can still be navigated to.