Use chrome_html structure for shared_resources and options2 page.

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 1002 matching lines @@
 
 span.bold {
   font-weight: bold;
 }
 
 .error-message {
   -webkit-padding-start: 30px;
   background-image: url('chrome://theme/IDR_WARNING');
   background-position: left top;
   background-repeat: no-repeat;
+  background-size: 24px;
 }
 
 .error-message-padding {
   margin-bottom: 10px;
 }
 
 html[dir=rtl] .error-message {
   background-position: right top;
 }
 
@@ skipping 20 matching lines @@
 }
 
 #notification-area a {
   color: rgb(37, 79, 155);
 }
 
 #notification-area .butter-bar {
   margin: 0 auto;
   max-width: 850px;
 }