[css-sizing] markup fix

Author: tabatkins

css-sizing-3/Overview.bs

@@ -141,7 +141,7 @@ Terminology</h2>
 <h3 id='auto-box-sizes'>
 Auto Box Sizes</h3>
 
-	<div export>
+	<dl export>
 		: <dfn>stretch-fit size</dfn>
 		: <dfn>stretch-fit inline size</dfn>
 		: <dfn>stretch-fit block size</dfn>
@@ -205,7 +205,7 @@ Auto Box Sizes</h3>
 
 			Note: This is called the “shrink-to-fit” width in <a href="https://www.w3.org/TR/CSS2/visudet.html#float-width">CSS2.1§10.3.5</a>
 			and <a href="https://www.w3.org/TR/css3-multicol/#pseudo-algorithm">CSS Multi-column Layout § 3.4</a>.
-	</div>
+	</dl>
 
 <h3 id='contributions' dfn export lt="intrinsic size contribution">
 Intrinsic Size Contributions</h3>