Improve accessibility of user image selection screen.

chrome/browser/resources/chromeos/login/oobe.css

 /* Copyright (c) 2012 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  * This is the stylesheet used by the Out of the box experience (OOBE) flow,
  * sign in and lock screens.
  */
 
 html,
 body {
@@ skipping 462 matching lines @@
   width: 400px;
 }
 
 #user-image-grid img {
   background-color: white;
   height: 50px;
   vertical-align: middle;
   width: 50px;
 }
 
-#user-image-grid [role=listitem] {
+#user-image-grid > li {
   border: 1px solid rgba(0, 0, 0, 0.15);
   border-radius: 4px;
   display: inline-block;
   margin: 4px;
   padding: 3px;
 }
 
 #user-image-grid [selected] {
   border: 2px solid rgb(0, 102, 204);
   padding: 2px;
@@ skipping 773 matching lines @@
   width: 100%;
 }
 
 .background-initial {
   opacity: 0;
 }
 
 .background-final {
   opacity: 1;
 }