Hey SJS!
I think 768 pixels is too wide to cover iphone size, please try the following instead, it will remove the caption from all screens which are wider than 1024 pixels:
@media only screen and (max-width: 1024px) {
.av-inner-masonry-content.site-background {
display: none !important;
}}
Regards,
Rikard
Perfect, thanks!