[css-ui-4] Change appearance: button to only apply to buttons

Closes w3c#5174

Author: frivoal

css-ui-4/Overview.bs

@@ -1766,7 +1766,7 @@ so this specification allows flexibility.
 
 <pre class="propdef">
 Name: appearance
-Value: ''appearance/none'' | ''auto'' | ''button'' | ''textfield'' | ''menulist-button'' | <<compat-auto>>
+Value: ''appearance/none'' | ''auto'' | ''textfield'' | ''menulist-button'' | <<compat-auto>>
 Initial: none
 Applies To: all elements
 Inherited: no
@@ -1847,16 +1847,6 @@ so that CSS can be used to restyle them.
 
 		Elements other than <a>widgets</a> must be rendered as if ''appearance/none'' had been specified.
 
-	<dt><dfn>button</dfn>
-	<dd>
-		The element is rendered with the look and feel of a push button,
-		similar to the ''appearance: auto'' rendering of the [[HTML]] <{button}> element.
-
-		UAs must treat this value as ''appearance/auto'' on <{input}> elements,
-		<{textarea}> elements, <a spec="html">list box</a> <{select}> elements, <{meter}> elements, and <{progress}> elements.
-
-		Note: Using ''appearance/button'' on a <a spec="html">drop-down box</a> <{select}> element works.
-
 	<dt><dfn>textfield</dfn>
 	<dd>
 		For <{input}> elements where the <{input/type}> attribute is in the Search state,
@@ -1881,7 +1871,7 @@ so that CSS can be used to restyle them.
 		for earlier non-standard versions of this property.
 		They all have the same effect as ''appearance/auto''.
 
-		<pre class=prod style="white-space: normal"><<compat-auto>> =  <dfn>searchfield</dfn> | <dfn>textarea</dfn> | <dfn>push-button</dfn> | <dfn>slider-horizontal</dfn> | <dfn>checkbox</dfn> | <dfn>radio</dfn> | <dfn>square-button</dfn> | <dfn>menulist</dfn> | <dfn>listbox</dfn> | <dfn>meter</dfn> | <dfn>progress-bar</dfn></pre>
+		<pre class=prod style="white-space: normal"><<compat-auto>> =  <dfn>searchfield</dfn> | <dfn>textarea</dfn> | <dfn>push-button</dfn> | <dfn>slider-horizontal</dfn> | <dfn>checkbox</dfn> | <dfn>radio</dfn> | <dfn>square-button</dfn> | <dfn>menulist</dfn> | <dfn>listbox</dfn> | <dfn>meter</dfn> | <dfn>progress-bar</dfn> | <dfn>button</dfn> </pre>
 
 		Issue: When ''appearance/auto'' is widely supported,
 		recommend using it instead.
@@ -1892,7 +1882,7 @@ so that CSS can be used to restyle them.
 
 		Issue: It is possible that for compat reasons
 		some of these values need to be promoted to being full blown values
-		with effects on arbitrary elements like ''button'',
+		with effects on arbitrary elements,
 		or that
 		some of these values need to have some side effects on some <a>widgets</a>.
 
@@ -2164,7 +2154,13 @@ In addition to a number of editorial adjustments,
 the following normative changes have been made:
 
 <ul>
-	<li>Defined user-select to be discretely animatable, rather than not
+	<li>
+		Defined user-select to be discretely animatable, rather than not
+
+	<li>
+		Restricted the applicability of ''appearance: button''
+		so that it can no longer give a buttony appearance
+		to widgets that aren't buttons to start with.
 </ul>
 
 <h3 id=changes-22-12-2017 class=no-num>Changes from the