[css-values-5][editorial] Add an example of style() being cyclic.

Author: tabatkins

css-values-5/Overview.bs

@@ -1390,6 +1390,12 @@ Conditional Value Selection: the ''if()'' notation</h3>
 				would be a [=cyclic substitution context=],
 				that query evaluates to false.
 
+				<div class=example>
+					For example, in ''--foo: if(style(--foo: bar): baz);''
+					the ''style()'' query is automatically false,
+					since [=property replacement=] has already established a &bs<<"property", "--foo"&bs>>; [=substitution context=].
+				</div>
+
 				If the result of |condition| is false,
 				[=iteration/continue=].