[css-overflow-3] Move clarifying sentence down into a note. Fixes w3c#5800.

Author: tabatkins

css-overflow-3/Overview.bs

@@ -532,16 +532,16 @@ Expanding ''overflow:clip'' Bounds: the 'overflow-clip-margin' property</h3>
 	<dl dfn-type=value dfn-for=overflow-clip-margin>
 		: <dfn><<length [0,∞]>></dfn>
 		::
-			If the element does not have ''overflow: clip''
-			(or another property defined to respect this property),
-			this property has no effect.
-
-			Otherwise, the specified length dictates
+			The specified length dictates
 			how much the [=overflow clip edge=] is expanded from the [=padding edge=],
 			in exactly the same way as a 'box-shadow' grows
 			due to a positive spread distance
 			(including the effect on rounded corners).
 			Negative values are invalid.
+
+			Note: If the element does not have ''overflow: clip''
+			(or another property defined to use the [=overflow clip edge=]),
+			this property has no effect.
 	</dl>
 
 <h3 id="overflow-propagation">