Login FancyBox

I’m try to replicate, from this website, the function of the “Members” button in the top right menu. How to get it opened through fancybox and the once logged in when you click members it show buttons linked to the WordPress back end. Any ideas? https://www.abandonedok.com/

I’ve tried linking the menu item to /wp-admin then adding class=”fancybox iframe” and class=”fancybox-iframe” to the style but nothing happened. Thoughts? Thanks in advance!

Here is a screen shot once you are logged in https://www.friendlymicfilms.com/wp-content/uploads/2013/04/AOK-CP.png