Bug 293845 – will-change: offset-position should create a stacking context

• Status: NEW
• Component: CSS

[Ahmad Saleem]

Hi Team,

While going through Blink's test cases for motion path, I noticed three failures but one was about following case:

Test Case Name - position-will-change-establishes-stacking-context.html

Test Case Link - https://jsfiddle.net/6xkwroL0/

^ Fails in WebKit ToT (295637@main) and Firefox Nightly 141 (20250528092647) while passes in Chrome Canary 139.0.7210.0 (Official Build) canary (arm64) .

This fixes in WebkIt:

> Source/WebCore/rendering/style/WillChangeData.cpp in function 'propertyCreatesStackingContext', add below:

    case CSSPropertyOffsetPosition:

This progresses above Blink test case.

Web Specification - https://drafts.fxtf.org/motion-1/#offset-position-property

Just raising here to see whether we need to fix or we should as Blink to match WebKit and Firefox.

Thanks1

[Sam Sneddon [:gsnedders]]

If we believe there's any web compat impact, we should raise a spec bug.

If we don't, we could at least write a WPT test that it _doesn't_ establish a stacking context so there's some failing test, and/or file a bug against Chromium.

[Radar WebKit Bug Importer]

<rdar://problem/152753709>