[html] How to replicate background-attachment fixed on iOS

I'm trying to get fixed-background-image divs working on iOS for a school project. I've been using

background-attachment: fixed;

But this is leading to weird sizing and no scrolling effects in mobile safari. Here is the site that I'm working with; the method I'm currently using for the quote div image backgrounds works well on desktops but fails completely on iOS.

Somehow, http://www.everyonedeservesgreatdesign.com got this working. I'm having difficulty following the code because they're using a squarespace template of some kind, but it looks like they're putting images into a position:fixed div that is somehow being clipped by its position:relative parent div. I was under the impression that it wasn't possible to clip position:fixed divs with anything other than the viewport, so I'm very curious as to what's going on here.

Any ideas on how to implement this method for fixed image div backgrounds in my site?

It looks to me like the background images aren't actually background images...the site has the background images and the quotes in sibling divs with the children of the div containing the images having been assigned position: fixed; The quotes div is also given a transparent background.

wrapper div{
   image wrapper div{
       div for individual image{ <--- Fixed position
          image <--- relative position
       }
   }
   quote wrapper div{
       div for individual quote{
          quote
       }
   }
 }