Problem home page on Apple

Hello! First: sorry for my bad english!
I’m using onetone on this site.
Thanks to Italian Forum, I added a them child with this instructions in style.css
section.home-section-1 {
background-size: cover !important;
background-attachment: fixed !important;
}
because I need to resize hp image on smartphone.
Now it’s ok in android but in iphone and ipad, I see black background… ??
Somebody can help me?
Thanks a lot!
valentina