[css-syntax-3][editorial] Whoops, I moved the dfn for at-rule and didn't adjust the previous location to stop dfn'ing it.

Author: tabatkins

css-syntax-3/Overview.bs

@@ -1648,9 +1648,9 @@ Parsing</h2>
 	The items that can appear in the tree are:
 
 	<dl export dfn-for=CSS>
-		<dt><dfn id="at-rule">at-rule</dfn>
+		<dt>[=at-rule=]
 		<dd>
-			An at-rule has a name,
+			An [=at-rule=] has a name,
 			a prelude consisting of a list of component values,
 			and an optional block consisting of a simple {} block.