Apply suggested changes from review

Co-authored-by: Tab Atkins Jr. <jackalmage@gmail.com>

Author: dlibby-

css-env-1/Overview.bs

@@ -188,7 +188,7 @@ In order to substitute the value of an [=environment variable=] into a CSS conte
 use the ''env()'' function:
 
 <pre class=prod>
-	<dfn function>env()</dfn> = env( <<custom-ident>> <<integer>>{0,2}, <<declaration-value>>? )
+	<dfn function>env()</dfn> = env( <<custom-ident>> <<integer [0,∞]>>*, <<declaration-value>>? )
 </pre>
 
 The ''env()'' function can be used in place of any part of a value in any property on any element,