[css-overflow-3] Mention at-riskness in note

Author: fantasai

css-overflow-3/Overview.bs

@@ -487,7 +487,8 @@ Scrolling and Clipping Overflow: the 'overflow-x', 'overflow-y', and 'overflow'
 	the recommended UA style sheet rules are to effect their original behavior as a default.
 	See discussion in <a href="https://github.com/w3c/csswg-drafts/issues/7058">Issue 7059</a>
 	and <a href="https://github.com/w3c/csswg-drafts/issues/7144">Issue 7144</a>.
-	This is a change from <a href="https://www.w3.org/TR/CSS2/">CSS2.1</a>.
+	This is a change from <a href="https://www.w3.org/TR/CSS2/">CSS2.1</a>
+	and is at-risk.
 
 <h3 id="static-media">
 Overflow in Print and Other Static Media</h3>