[Webkit-unassigned] [Bug 239357] New: Element with "position: sticky" doesn't stick if parent element has "contain: paint"

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=239357

            Bug ID: 239357
           Summary: Element with "position: sticky" doesn't stick if
                    parent element has "contain: paint"
           Product: WebKit
           Version: Safari 15
          Hardware: Mac (Intel)
                OS: macOS 12
            Status: NEW
          Severity: Minor
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: danilu at adobe.com

Reproduction Steps:
1. Go to https://codepen.io/dl1644/pen/zYpmLpd in Safari 15.4 (macOS 12.3.1)
2. Attempt to scroll the green/yellow/red div to the right
3. Note that the green "sticky" div is scrolled out of view
4. Repeat steps 1 and 2 in Chrome(100) and Firefox (99). Note that the green "sticky" div stays in view
5. Return to your Safari codepen tab and remove "contain: paint" from the "#row" CSS
6. Attempt to scroll the green/yellow/red div. Note that the green "sticky" div stays in view now but the yellow "float" div now spills out the bottom of the red div


Started occurring with Safari 15.4 from what I can tell. Unsure if this counts as a regression since "contains" is newly supported in Safari 15.4 but the sticky behavior worked just fine in at least Safari 14 and below.

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