[css-values] fix markup

Author: tabatkins

css-values/Overview.html

@@ -1428,11 +1428,13 @@ <h2 id=functional-notation><span class=secno>8. </span> Functional
    would be ambiguous otherwise. If a comma is used to separate arguments,
    whitespace is optional before and after the comma.
 
-  <pre class=example>
+  <div class=example>
+   <pre>
 <!-- -->background: url(http://www.example.org/image);
 <!-- -->color: rgb(100, 200, 50 );
 <!-- -->content: counter(list-item) ". ";
 <!-- -->width: calc(50% - 2em);</pre>
+  </div>
 
   <h3 id=calc-notation><span class=secno>8.1. </span> Mathematical
    Expressions: ‘<a href="#calc"><code class=css>calc()</code></a>’</h3>

css-values/Overview.src.html

@@ -958,11 +958,13 @@ <h2 id="functional-notation">
 		If a comma is used to separate arguments,
 		whitespace is optional before and after the comma.
 
-	<pre class="example">
+	<div class="example">
+		<pre>
 <!-- -->background: url(http://www.example.org/image);
 <!-- -->color: rgb(100, 200, 50 );
 <!-- -->content: counter(list-item) ". ";
 <!-- -->width: calc(50% - 2em);</pre>
+	</div>
 
 <h3 id="calc-notation">
 Mathematical Expressions: ''calc()''</h3>