Need help with ideas on design interactions for Nav Bar

Hey there

I need some help attempting to get the same effect on the nav bar that is on the site bellow:

Not sure really where to start with this but i wish to have my page, which is designed the same from face value achieve the same effect. It’s almost as when the box and nav scroll out of view, the Nav changes to white from black.

Any ideas how to achieve this?


Here is my public share link: LINK
(how to access public share link)