thanks for the reply. Basically, I want to achieve 2 things:
1. transparency upon scroll. I’m not sure if it’s the header or menu/nav (in apple.com homepage)
2. there’s a 2nd layer of menu in https://www.apple.com/iphone-x/, so that when you scroll, the first menu (the dark grey) disappears so that what is left is only the menu that is white/transparent.