I’ll be more precise here - I hope I’m aligned with OP’s intent - let me know if I should take my question to a separate thread:
My page has a background photo and some foreground items, which produce a very nice parallax effect. When using Chrome on Windows, I can reduce the viewing area at will - to a size way narrower than my mobile, for example - and I still get a perfect parallax (nicely reduced to the visible area size). Moreover, Chrome now has a feature to actually emulate all kinds of phones and tablets for you (within the Inspect feature) - very nice. No matter which phone I emulate (Nexus 6P, iPhone 5, iPhone 6…) I get a perfectly played parallax.
Until I go to an actual mobile phone. There, no parallax. Everything scrolls in sync - foreground and background.
This is weird (as I don’t understand the media query that would account for this difference) and I’m quite at loss as to how I can fix it.