iOS not respecting z-index with -webkit-overflow-scrolling
Problem:
On iOS the z-index of a scrollable area is ignored when using -webkit-overflow-scrolling. If two objects with -webkit-overflow-scrolling overlap the lower one is scrolled instead of the one being displayed above.
How to reproduce:
Create two elements overlaying each other (with position: absolute for example), one of them having a higher z-index and add
.selector
{
overflow-y: auto;
-webkit-overflow-scrolling: touch;
}
to both of them. Both elements should have enough content to be scrollable.
Additionally add
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-status-bar-style" content="black">
to your <head>. Then add the page to your home screen and launch it from there.
If you then try to scroll the upper element the element beneath is scrolled instead.
MCVE:
Alternatively just check out this pen. Launch the full version from your iOS device, add it to your home screen and launch from there.
Environment:
Tested on iPhone 5 and iPhone 6 with iOS 9.1 and iOS 9.3.2
Observations:
- The issue only occurs when launching the page/app from homescreen (pinned app) or inside a Xamarin Webview (might have something to do with UIWebView and WKWebView)
- After changing the device orientation (portrait/landscape) after page load the problem is fixed until the page is reloaded (maybe re-triggering layout fixed it?)
- Changing the lower elements
overflow-ytohiddenvia JS does fix the problem, however togglingoverflowcauses a repaint causing performance issues - Removing
height: 100%; width: 100%fromhtml, bodyfixes the problem as well, however those have to be set for percentage values to work properly
Needed is a proper solution / workaround to fix this issue without causing any troublesome side-effects. Also explanation of why this happens would be appreciated.
Answer
Essentially, what you're experiencing is an iOS bug with -webkit-overflow-scrolling: touch;. In order to solve this bug, as per this answer, just add the following CSS styles to the scrollable div:
-webkit-transform: translateZ(0px);
-webkit-transform: translate3d(0,0,0);
-webkit-perspective: 1000;
So all in all, if you add the above styles to the styles for the scrollable class in your CSS, it should work. Tested on an iPhone 5s running iOS 9. Note that if you scroll down to the bottom or top of the scrollable section that is above everything else, it will start to scroll the body.
I believe that what those extra styles do is trick the iPhone into using the GPU, but remember that they're only necessary due to a bug with Safari - it's not your fault and these extra styles shouldn't really need to be included. But pop them into your CSS and it should work like a dream!