What are the steps required to reproduce the bug?
Open a "dialog" which contains an iframe which overflows the height of the dialog using iOS 8+ Safari (replicated in iOS 10 on an iPad Pro).
This issue was originally noticed when using Entity Browser (see https://www.drupal.org/node/2781873 → ). This uses an iframe inside a dialog which, on iOS, is not scrollable. You therefore can't view all the items in the browser or use the submit buttons at the bottom.
What behavior were you expecting? To be able to scroll the dialog iframe as you would on a desktop device.
What happened instead? Could not scroll the iFrame (although if you select the very edge of the dialog you can scroll), whole page attempts to scroll instead.
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Adding -webkit-overflow-scrolling: touch; to the dialog content fixes this issue. It also enables iOS's momentum scrolling for that element (patch to follow).
Needs review
1.0
Code
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