Header / Slideshow Gallery

Hey. So I really like the look of a background image behind my header with my logo and navigation titles on top of it and I am trying to make it so the background is a fading slideshow and not just one photo behind it. I made a gallery slideshow but when I go to move up to the top it doesn't lay under my header like a background would. I understand that the gallery slideshow is an image block and different than a background but I wondered if there is any way to make it work? This is the look I am going for: https://www.kendalanne.com/

Thanks!

The plugin I mention in this post on full bleed slideshows also allows header overlay: 

https://christyprice.com/squarespace-tips-tricks/full-bleed-slideshow