Bug 301510 – [CSS @starting-style] entry animation is only respected on first transition

• Status: RESOLVED
• Resolution: FIXED
• Component: Layout and Rendering

hey there, raising this off of another one raised last week

i've noticed that @starting-style entry/exit transitions aren't being respected as expected. not sure if this is a regression as i haven't seen this happen before (much like the issue i had with showing the non-modal dialog in the other issue i filed)

Steps to Reproduce:
1. open the demo: https://codepen.io/jh3y/pen/RNrJEbw/b560906a4c78fda2f390fec86878e56f
2. open the dialog, note how the transform-origin is respected on the transition
3. close the dialog, note how it's a different transition
4. reopen the dialog, notice how the entry transition is now ignored and the exit is being reversed instead

Actual Results:
– entry transition is only respected on first play through

Expected Results:
– the entry and exit transitions should be respected on each playthrough

[Alexey Proskuryakov]

Thank you for the report, I can reproduce with STP 230.

> not sure if this is a regression as i haven't seen this happen before

Could you please elaborate? The dialog appears to be anchor-positioned, so the test relies on a new feature in Safari 26. Are you using a newer build, and unsure if this is a regression since Safari 26?

(In reply to Alexey Proskuryakov from comment #1)
> Thank you for the report, I can reproduce with STP 230.
> 
> > not sure if this is a regression as i haven't seen this happen before
> 
> Could you please elaborate? The dialog appears to be anchor-positioned, so
> the test relies on a new feature in Safari 26. Are you using a newer build,
> and unsure if this is a regression since Safari 26?

i figured this issue was related to @starting-style and i'm sure that's been around since before v 26 unless this is specific to the way dialog behaves? i was using popovers previous to this 🙏

[Radar WebKit Bug Importer]

<rdar://problem/163928932>

[Antoine Quint]

This is likely going to be a similar issue or a duplicate of bug 301461. I expect this is only happening with anchor positioning and starting style mixed together.

[Kiet Ho]

Might be fixed by bug 301461.

[Kiet Ho]

Pull request: https://github.com/WebKit/WebKit/pull/53392

[EWS]

Committed 305371@main (d9149b628100): <https://commits.webkit.org/305371@main>

Reviewed commits have been landed. Closing PR #53392 and removing active labels.