at-rule()The at-rule() function, when used with @supports, checks if a CSS at-rule is supported. For example @supports at-rule(@starting-style) checks if the @starting-style at-rule is supported.cssCSSlimitedhttps://drafts.csswg.org/css-conditional-5/#typedef-supports-at-rule-fnhttps://developer.mozilla.org/docs/Web/CSS/Reference/At-rules/@supportscss.at-rules.supports.at-rulehttps://nowyoucanuse.com/features--supports-at-rule.html