Fix typo

Author: ranma42

css-gcpm-3/Overview.bs

@@ -304,7 +304,7 @@ CSS:
 
 
 
-<p class="note">The element ''value()'' can only be used in page margin boxes. And it cannot be combined with other possible values for the content property.</p>
+<p class="note">The ''element()'' value can only be used in page margin boxes. And it cannot be combined with other possible values for the content property.</p>
 <div class="issue">
 <p>This idea would be much more useful if we could also copy (rather than just move) elements. That would avoid the duplication of HTML in the example above.
 </p>