[Webkit-unassigned] [Bug 254590] REGRESSION (Safari 16.4): Behavior of transform:scale(0), Polyglot extension popup disappears

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=254590

Razvan Caliman <rcaliman at apple.com> changed:

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                 CC|                            |rcaliman at apple.com

--- Comment #6 from Razvan Caliman <rcaliman at apple.com> ---
Copying over some notes from Bug 254585 which is related to this one:

This has been progressed in Safari 16.4, not regressed. 

The issue with the disappearing popup is caused by the animation of a property marked `!important`.

Simplified test case extracted from: https://github.com/uetchy/Polyglot/blob/master/PolyglotSafariExtension/ContentScript/content.css

```
#polyglot__panel {
   transform: scale(0) !important;
...
   animation: polyglot__envelope 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275)
              forwards !important;
}

@keyframes polyglot__envelope {
  0% {
    transform: scale(0);
  }
  100% {
    transform: scale(1);
  }
}
```

The animation fill mode `forwards` isn't kept. The style that wins at the end is `transform: scale(0) !important;`. This is intentional. Therefore, the panel disappears because it scales back to zero right after the animation ends.

The animation itself should not run at all. This is being addressed in Bug 254665.

It is a fix to bring WebKit in line with the intended spec behavior which is respected by other browser engines. See also Bug 252481. The fact that this worked in previous Safari versions was itself a bug.

---

The issue with Web Inspector not reflecting the correct applied styles is valid and tracked in Bug 254585.

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