Wrong code? Resizing background images for mobile

Hi there. I know there are several threads on this but I've tried multiple sets of code and cannot figure it out. I'd like to resize all of my section background images for mobile. I was able to implement this when I was using background videos - but can't figure it out for imagery. Is there css to resize ALL background imagery to be optimized for mobile or do I have to go one section at a time? Also, maybe someone can look at my code to see if I've made a mistake somewhere?

https://hibiscus-dachshund-wk7b.squarespace.com/config/

pw: forumhelp2

Hi,

#1. You mean top image on homepage?

#2. Can you paste code here?

The code is show on browser, will different with code show in CSS box

I'm having the same trouble. I want all the background images for all my sections to be resized to fit into a mobile view.