[css-color-5] Add missing color-mix to grammar of <color>, #9445

Author: svgeesus

css-color-5/Overview.bs

@@ -123,7 +123,7 @@ Introduction {#intro}
 	Colors in CSS are represented by the <dfn export><<color>></dfn> type:
 
 	<pre class='prod'>
-	&lt;color> = <<absolute-color-base>> | currentcolor | <<system-color>> | <<device-cmyk()>> | <<light-dark()>>
+	&lt;color> = <<absolute-color-base>> | currentcolor | <<system-color>> | <<device-cmyk()>> | <<color-mix()>> | <<light-dark()>>
 
 	<dfn>&lt;absolute-color-base></dfn> = <<hex-color>> | <<absolute-color-function>> | <<named-color>> | transparent
 	<dfn>&lt;absolute-color-function></dfn> = <<rgb()>> | <<rgba()>> |