Use chrome_html structure for shared_resources and options2 page.

chrome/browser/resources/options2/content_settings.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. */
 
 #content-settings-page {
   min-width: 600px;
 }
 
 #content-settings-exceptions-area {
   min-width: 540px;
@@ skipping 53 matching lines @@
 
 .settings-list div[role='listitem'][managedby='policy'],
 .settings-list div[role='listitem'][managedby='extension'] {
   background: -webkit-linear-gradient(rgb(250, 230, 146), rgb(250, 230, 146));
   border-bottom: 1px solid rgb(201, 189, 141);
   border-top: 0;
 }
 
 list div[role='listitem'][managedby='policy'] .close-button {
   background-image: url('chrome://theme/IDR_MANAGED');
+  background-size: 16px;
   opacity: 1;
 }
 
 list div[role='listitem'][managedby='extension'] .close-button {
   background-image: url('chrome://theme/IDR_EXTENSIONS_SECTION_SMALL');
+  background-size: 16px;
   opacity: 1;
 }