[Collapsible] Opacity starting style not working

[benface]

Bug report

Current behavior

The following Tailwind classes in Collapsible.Panel lead to a fade out transition when the panel closes, but no fade in transition when it opens:

transition data-[starting-style]:opacity-0 data-[ending-style]:opacity-0

Expected behavior

There should be a fade in transition when the panel opens.

Reproducible example

https://codesandbox.io/p/sandbox/winter-cdn-vxmxzn

Base UI version

1.0.0-alpha.5

Which browser are you using?

Reproduced in Chrome, Firefox, and Safari

Which OS are you using?

macOS

Which assistive tech are you using (if applicable)?

None

Additional context

Thank you! 🙏