[css-forms-1] Fix markup

Author: cdoublev

css-forms-1/Overview.bs

@@ -138,12 +138,12 @@ Markup Shorthands: css yes, markdown yes
 
   <pre class=prod>
     ::picker() = ::picker( <<form-control-identifier>>+ )
-    <<form-control-identifier>> = select
+    <dfn for="::picker()"><<form-control-identifier>></dfn> = select
   </pre>
 
   The ''::picker()'' pseudo-element only matches when the [=originating
   element=] supports [=basic appearance=] and has a popup picker. The
-  specified <<ident>> must also match the <dfn>unique picker name</dfn> of the
+  specified <<form-control-identifier>> must also match the <dfn>unique picker name</dfn> of the
   [=originating element=]. For example, the [=unique picker name=] for
   the <{select}> element is ''select''.