[css-values-3][editorial] Changes not normative, fix w3c#8120

Author: svgeesus

css-values-3/Overview.bs

@@ -2232,7 +2232,7 @@ Acknowledgments</h2>
 	and Michael Day
 	improved this module.
 
-
+<div class="informative">
 <h2 class="no-num" id="changes">
 Changes</h2>
 
@@ -2382,6 +2382,7 @@ Changes</h2>
 		<li>Clarified definition of ''ex'' to refer to the “first available font”.
 		<li>Specified that ''attr()'' with ''string'' or ''url'' types doesn't reparse the attribute contents, just takes the value literally as the value of a <<string>>.
 	</ul>
+</div>
 
 <h2 class="no-num" id="security">
 Security Considerations</h2>