[css-overflow-3] Markup tweak

Author: fantasai

css-overflow-3/Overview.bs

@@ -175,11 +175,10 @@ Scrollable overflow</h3>
 			Issue: Need to evaluate compat of honoring or ignoring 'clip' and 'clip-path'.
 	</ul>
 
-	<p>Additionally, the UA <em>may</em> <em>additionally</em> include
+	Additionally, the UA may <em>additionally</em> include
 	the margin areas of boxes for which it is the containing block.
 	The conditions under which such margin areas are included is undefined in this level.
-
-	Issue: This needs further testing and investigation; is therefore deferred in this draft.
+	<span class="issue">This needs further testing and investigation; is therefore deferred in this draft.</span>
 	<!--
 	Considerations:
 	  * floats