[css-mixins-1] Revert to ED (#12374)

Also, fix a markup problem which made the parser unhappy in section 7.1.2.

Author: andruud

css-mixins-1/Overview.bs

@@ -2,9 +2,8 @@
 Title: CSS Functions and Mixins Module
 Shortname: css-mixins
 Level: 1
-Status: FPWD
-Date: 2025-05-15
-Prepare for TR: yes
+Status: ED
+Prepare for TR: no
 Work Status: Exploring
 Group: CSSWG
 ED: https://drafts.csswg.org/css-mixins/
@@ -1396,7 +1395,7 @@ but ''env()'' can be used in locations that don't have an element context.
 	an ''em'' value is passed to a mixin,
 	but the argument is then used in the ''@media'' rule inside the mixin.
 
-	<pre highlight=css>
+	<xmp highlight=css>
 	@mixin --smaller(--size <length>: 800px, @contents) {
 		@media (width <= env(--size)) {
 			@contents;
@@ -1407,7 +1406,7 @@ but ''env()'' can be used in locations that don't have an element context.
 			margin: 1em 0;
 		}
 	}
-	</pre>
+	</xmp>
 </div>
 
 When this situation occurs,