[css-variables] Slightly reword and expand on the 'custom proeprties are case-sensitive' statement.

Author: tabatkins

css-variables/Overview.html

@@ -13,7 +13,7 @@
    content="CSS Custom Properties for Cascading Variables Module Level 1"
    name=dcterms.title>
   <meta content=text name=dcterms.type>
-  <meta content=2013-02-27 name=dcterms.issued>
+  <meta content=2013-02-28 name=dcterms.issued>
   <meta content="http://dev.w3.org/csswg/css-variables/"
    name=dcterms.creator>
   <meta content=W3C name=dcterms.publisher>
@@ -31,7 +31,7 @@
 
    <h1>CSS Custom Properties for Cascading Variables Module Level 1</h1>
 
-   <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 27 February
+   <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 28 February
     2013</h2>
 
    <dl>