*Summary*:
The CSS *at-rule()*
<https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/At-rules/@supports#at-rule>
function for the *@supports*
<https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/At-rules/@supports>
at-rule
allows authors to detect browser support of specific at-rules. It can also
be used with the *CSS.supports()
<https://developer.mozilla.org/en-US/docs/Web/API/CSS/supports_static>*
JavaScript
method as well as in the *supports()
<https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/At-rules/@import#supports-condition>*
function
of the *@import*
<https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/At-rules/@import>
at-rule. Together, these allow authors to conditionally write styles or
execute code depending on browser support for specific at-rules. For
example:
/* Conditional styles */
@supports at-rule(@scope) {
@scope { /* ... */ }
}
/* Conditional import */
@import "props.css" supports(at-rule(@property));
/* Feature detection in JavaScript */
if (CSS.supports("at-rule(@view-transition)")) { }
We intend to enable these functions in *Firefox Nightly* builds behind the
*layout.css.supports.at-rule.enabled* pref.
*Bug*:
Bug 1751188 - Implement at-rule for use with @supports
<https://bugzilla.mozilla.org/show_bug.cgi?id=1751188>
*Specification*:
https://drafts.csswg.org/css-conditional-5/#funcdef-supports-at-rule
*Standards Body*:
CSSWG / W3C
*Platform Coverage*:
All
*Preference*:
*layout.css.supports.at-rule.enabled* — Bug 2060754
<https://bugzilla.mozilla.org/show_bug.cgi?id=2060754> to implement and
enable in Nightly
*DevTools Bug*:
N/A (supported by default in the at-rules panel of the Style Editor)
*Extensions Bug*:
N/A
*Use Counter*:
N/A
*Standards-Positions Discussion*:
https://github.com/mozilla/standards-positions/issues/1310 — (no position)
*Other Browsers*:
- Blink: Shipped since Chrome 148
- WebKit: Implementation in progress (
https://bugs.webkit.org/show_bug.cgi?id=235400)
*web-platform-tests*:
https://wpt.fyi/results/css/css-conditional/js/supports-at-rule.html — Also
adding an additional WPT file to test serialization of the *at-rule()*
function.
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