How to create a slide away site header

Hi There

I came across a Squarespace template site that utilizes a 'side away' header. Here's the link: Nolan & Co (squarespace.com) Notice when you scroll down the header slides up, and when you scroll to the top the header slides back into view. 

I can't find any standard elements in the site header design tools that allow me to create this. Would love to know how to accomplish this. 

Regards

Sam

First, edit Site Header

Next, enable this option

Choose Scroll Back