Slightly improve example to make the case it illustrates clearer.

Author: tabatkins

css-variables/Overview.html

@@ -408,8 +408,9 @@ <h2 id=defining-variables><span class=secno>2. </span> Defining Variables
 }</pre>
 
    <p> The ‘<code class=property>var-accent-background</code>’ property
-    will automatically update when the ‘<code
-    class=property>var-main-color</code>’ property is changed.
+    (along with any other properties that use ‘<code
+    class=css>$main-color</code>’) will automatically update when the
+    ‘<code class=property>var-main-color</code>’ property is changed.
   </div>
 
   <div class="example invalid-example">

css-variables/Overview.src.html

@@ -266,7 +266,9 @@ <h2 id="defining-variables">
 }</pre>
 
 		<p>
-			The 'var-accent-background' property will automatically update when the 'var-main-color' property is changed.
+			The 'var-accent-background' property 
+			(along with any other properties that use ''$main-color'')
+			will automatically update when the 'var-main-color' property is changed.
 	</div>
 
 	<div class='example invalid-example'>