I need to figure out how to make a banner image static in the background while my images/text go on top of it and scroll...

I'm trying to get the banner image on my site become static on the background while the other stuff sits on top of it and moves. Similar to the effect on this page: https://www.takemeoutofoffice.com/

But no matter what code I've tried, I can't seem to figure it out! Would love any insight or code or links to other threads that people have had success with. thank you!!

I am trying to figure out how to get part of an image to hide behind the bottom of a section break - similar to the top iphone image on the banner of this page: https://www.takemeoutofoffice.com/

I've tried about a dozen different attempts at CSS but none have worked. Would love any wisdom or code blocks or links to other threads that people have had success with using. Thank you!!