AtRule supports feature detection

[diekus]

WebKittens

@fantasai

Title of the proposal

CSS AtRule

URL to the spec

https://www.w3.org/TR/css-conditional/

URL to the spec's repository

https://github.com/MicrosoftEdge/MSEdgeExplainers/tree/main/AtRuleFeatureDetection

Issue Tracker URL

https://github.com/MicrosoftEdge/MSEdgeExplainers/issues?q=state%3Aopen%20label%3AAtRuleFeatureDetection

Explainer URL

https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/AtRuleFeatureDetection/explainer.md

TAG Design Review URL

No response

Mozilla standards-positions issue URL

No response

WebKit Bugzilla URL

No response

Radar URL

No response

Description

Feature detection is a W3C TAG design principle and a tool that Web authors rely on for graceful degradation of their pages.

CSS Conditional Rules introduces the @supports rule and API extensions to allow authors to feature-detect CSS properties. In this explainer, we describe an expansion to feature detection in CSS that allows authors to detect support for at-rules, including specific features of at-rules.