pflombard

If you share your page I can get the actual code, but it will be something like
#collection #header { position: fixed; }  

Thanks so much rwp! This put me on the right path.

I found the collection-id for that specific page. 

This is the end result that worked just great.
#collection-5ef47e01a0680c5b1a28ecac #header {   position: fixed !important;   z-index: 1000; //in case it scrolls behind certain elements further down.   background: #df4430; //because header was transparent. }