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Anchor positioning (transforms and animations) #1457
Description
Description
After two rounds of anchor positioning focus areas in Interop 2025 and 2026, the following gaps remain:
- Positioned elements should correctly respond to transformed anchors.
- Positioned elements should correctly respond to transitioned/amnimated anchors.
Specification
https://drafts.csswg.org/css-anchor-position-1/
web-feature
web-features: anchor-positioning-transforms
web-features: anchor-positioning-animations
Test Links
- Transform: https://wpt.fyi/results/css/css-anchor-position?label=master&label=experimental&aligned&q=transform
- Animation: I think that's https://wpt.fyi/results/css/css-anchor-position?label=master&label=experimental&aligned&q=transition but there could be others.
Additional Signals
- According to the State of CSS 2026, anchor positioning is both developers' favorite new feature and the number 1 feature they avoid because of lack of support or differences between browsers.
- The anchor positioning developer signals issue is the second most upvoted issue on the repo, with 257 👍🏻, only second to JPEG XL, showing large interest in the feature overall.
- There's an entire ecosystem of JavaScript libraries that exist solely to solve the lack of anchor positioning support in the platform (e.g. Floating UI 32.8k stars and 1.7k forks). Libraries like this demonstrate how widespread this UI requirement is, and we owe it to developers to provide a complete and consistent implementation for it.
Activity
github-actions commentedon Sep 23, 2026
This comment was automatically generated based on the information you provided. Please don't edit it.
Below is additional information about the web features (from the web-features project) which are referenced in your proposal.
If this doesn't accurately correspond to your proposal, please update your initial comment to include
web-features: <feature-id>.To find feature IDs, use the web-features explorer.
Anchor positioning transforms
Feature Anchor positioning transforms
Anchor positioning animations and transitions
Feature Anchor positioning animations and transitions
anchor()andanchor-size()CSS functions animate or transition on changes such as the anchor box moving or the anchor element changing.jpzwarte commentedon Sep 23, 2026
Perhaps also include position-anchor: match-parent? I recently added WPT tests for it.
yisibl commentedon Sep 24, 2026
Firefox does not currently support anchor positioning on certain pseudo-elements; I think this should also be included in Interop 2027.
See: https://bugzilla.mozilla.org/show_bug.cgi?id=1993699
emilio commentedon Oct 8, 2026
The animation stuff is still pretty problematic spec-wise (e.g. w3c/csswg-drafts#11562)
emilio commentedon Oct 8, 2026
(The transforms I don't have a problem with)