[css-gcpm-3] Fix typo in the definition of running and element functions

Author: renatahodovan

css-gcpm-3/Overview.bs

@@ -254,7 +254,7 @@ The ''running()'' value
 
 
 <pre class="prod">
-	<dfn>running()</dfn> = string( <<custom-ident>> )
+	<dfn>running()</dfn> = running( <<custom-ident>> )
 </pre>
 
 <!--
@@ -366,7 +366,7 @@ Just as with ''string()'', ''element()'' takes an optional keyword to describe w
 </pre>
 
 <pre class="prod">
-	<dfn>element()</dfn> = string( <<custom-ident>> [ , [ first | start | last | first-except] ]? )
+	<dfn>element()</dfn> = element( <<custom-ident>> [ , [ first | start | last | first-except] ]? )
 </pre>
 
 <h2 id="footnotes">