Under "Manage>Privileges", you can select wether you want to edit the perms of a category, or the perms of "global".
You have to go to every category and edit the "guests" so all the boxes are unchecked.
I dunno if this is the correct place to ask, but I'd like to hire someone to make a custom theme. It's nothing radical, and the design mockups are all done. Just need someone to turn it into LESS and do the templating really (not looking for just a CSS skin).
Please send me a message here, or to my email address @ email@example.com // there's also an advertisement on Upwork.com if you'd like to use their system, just search NodeBB.