[Webkit-unassigned] [Bug 160953] WebKit incorrectly clips position:fixed element, inside of its "position:relative; overflow: hidden" parent, IF that parent has "z-index" set

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=160953

Ilya Konrad <ilyakonrad.drums at gmail.com> changed:

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                 CC|                            |ilyakonrad.drums at gmail.com

--- Comment #20 from Ilya Konrad <ilyakonrad.drums at gmail.com> ---
I can still reproduce it in a setup where an ancestor (A) has "overflow: hidden auto" (or "overflow-y: auto") with "position: relative", its deep descendant (B) has "position: absolute" with "z-index" and its deep descendant (C) has "position: fixed".

The "fixed" child block is clipped by the ancestor A for no reason, atrociously breaking the layout.

If I remove "position: relative" or the overflow rule from A - it works ok. The same is true if I remove "z-index" from B. However, obviously, I need all of them.

I checked a lot of provided examples of similar issues on real iPhone 13 (using Chrome, Safari and Firefox) and on Mac (using Safari and Chrome through Browserstack).

It seems to be an issue with all iOS devices and with Safari on Mac.

However only the example provided by Stefan (https://bugs.webkit.org/attachment.cgi?id=323520) has the same consistently broken behavior on different systems as my app.
Other examples (jsfiddles, codepens, etc.) work ok through Browserstack. Although maybe it's a Browserstack issue :/

Seems really critical, I'm surprised to see so few reports over all these years.

Is there a workaround? Is the bug being worked on? What can I do to help?

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