Allow opting out of button layout with appearance:none; display:inline

Fixes w3c/csswg-drafts#3226

source

@@ -113134,9 +113134,15 @@ input[type=image i][align=bottom i], object[align=bottom i] {
   <h4>The <code>button</code> element</h4>
 
   <p>The <code>button</code> element, when it generates a box (i.e., is not 'display: none' or
-  'display: contents') is expected to depict a button and to use <span>button layout</span> whose
-  <span>anonymous button content box</span>'s contents (if there is an <span>anonymous button
-  content box</span>) are the child boxes the element's box would otherwise have.</p>
+  'display: contents') and the conditions below do not both apply is expected to depict a button
+  and to use <span>button layout</span> whose <span>anonymous button content box</span>'s contents
+  (if there is an <span>anonymous button content box</span>) are the child boxes the element's box
+  would otherwise have.</p>
+
+  <ul class="brief">
+   <li>The <span>computed value</span> of <span>'display'</span> is 'inline'</li>
+   <li>The <span>computed value</span> of 'appearance' is 'none'</li>
+  </ul>
 
   </div>