Make 'button' act like 'auto' for list box <select>s

This uses terms defined in
whatwg/html#4312

Author: zcorpan

css-ui-4/Overview.bs

@@ -1844,9 +1844,9 @@ Animation type: discrete
 		similar to the ''appearance: auto'' rendering of the [[HTML]] <{button}> element.
 
 		UAs must treat this value as ''appearance/auto'' on <{input}> elements,
-		<{textarea}> elements, <{meter}> elements, and <{progress}> elements.
+		<{textarea}> elements, <a spec="html">list box</a> <{select}> elements, <{meter}> elements, and <{progress}> elements.
 
-		Note: Using ''appearance/button'' on a <{select}> element works.
+		Note: Using ''appearance/button'' on a <a spec="html">drop-down box</a> <{select}> element works.
 
 	<dt><dfn type="">&lt;compat></dfn>
 	<dd>