Intent to Prototype: CSS top-layer property

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Rune Lillesveen

Feb 3, 2023, 3:56:55 AMFeb 3
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Introduce a top-layer property to allow authors to keep elements in the top layer for an exit transition. The top-layer property is added to indicate if an element is in the top layer or not. It can take two values: 'none', 'browser'. User agent stylesheets add !important rules to control whether elements are rendered in the top layer or not, and not let author styles override. However, authors can add top-layer to the list of transition-properties for an element to defer the removal from the top-layer for the duration of the transition. That way the author can do exit transitions for elements like dialogs: transition-property: top-layer transition-duration: 0.4s

Blink component



It is currently not possible for authors to do exit transitions of things like modal dialogs in the top layer because the elements are immediately removed from the top layer. Adding this property will allow for authors to defer the removal while running a CSS transition.

Initial public proposal

TAG review

TAG review status



Interoperability and Compatibility

Gecko: No signal

WebKit: No signal

Web developers: No signals

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?


Is this feature fully tested by web-platform-tests?


Flag name

Requires code in //chrome?


Tracking bug

Estimated milestones

No milestones specified

Link to entry on the Chrome Platform Status

This intent message was generated by Chrome Platform Status.

Rune Lillesveen

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