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[css-anchor-position] Make position-area discretely animatable, for now. #13577
Description
The css-anchor-position-1 spec defines the animation type of position-area as:
TBD
This is leading to inconsistencies across browsers:
- Safari and Chrome: the property animates discretely
- Firefox: the property does not animate
Still allowing a possible future custom description for how it should animate (the magic in #9598 (comment) for the L2 spec), I think we should define it as discretely animatable until then.
This would remove the cross-browser inconsistency and also unlock animating from one position-area to another using View Transitions with a StyleObserver, as shown in this demo (which currently doesn’t work in Firefox): https://codepen.io/bramus/full/myrJYQz/b6aace5cc714e3147f81a2a1b4ed10f4
Activity
bramus commentedon Mar 2, 2026
I checked Stylo and
position-areais defined as discretely animatable (so the behavior I saw is most likely a bug)We should still update the spec though, so that it lines up with what browsers have implemented.
bramus commentedon Mar 18, 2026
@fantasai Is this considered “Editor’s discretion” or do we need a more formal (async) resolution?
[css-anchor-position-1] Mark position-area as animatable #13577
fantasai commentedon Mar 27, 2026
@bramus Done, thanks for filing!