[css-overflow-3] Tweak exported term

Author: fantasai

css-overflow-3/Overview.bs

@@ -530,9 +530,9 @@ Managing Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h3
 	</dl>
 
 	The ''overflow/scroll'', ''overflow/auto'', and ''overflow/hidden'' values
-	are known as the <dfn export for=overflow>scrollable values</dfn> of 'overflow'.
+	are known as the <dfn export lt="scrollable overflow value">scrollable values</dfn> of 'overflow'.
 	The  ''overflow/visible'' and ''overflow/clip'' values
-	are known as the <dfn export for=overflow>non-scrollable values</dfn>.
+	are known as the <dfn export lt="scrollable overflow value">non-scrollable values</dfn>.
 
 	The  ''visible''/''overflow/clip'' values of 'overflow'
 	compute to ''overflow/auto''/''hidden'' (respectively)