Brand Header making main header jerky on scroll

[jtbayly]

Same issue as discussed (and fixed) here?

How to finely scroll out custom header?

I see the top header of discourse.ubuntu.com and when I scroll down, the extra header smoothly scrolls out. Unlike other discourse forums like: https://talk.turtlerockstudios.com Notice the glitchy behaviour of the top nav. bar Can you provide the HTML and CSS code for the Ubuntu’s forum? with smooth transitioning