Replace IDR_WEB_UI_CLOSE* with IDR_CLOSE_DIALOG*, cleanup, etc.

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 1304 matching lines @@
   white-space: pre-line;
 }
 
 .oauth-enroll-link {
   color: -webkit-link;
   cursor: pointer;
   text-decoration: underline;
 }
 
 .close-button {
-  background: url('chrome://theme/IDR_WEB_UI_CLOSE') center no-repeat;
+  background: url('chrome://theme/IDR_CLOSE_DIALOG') center no-repeat;
   height: 14px;
   position: absolute;
   right: 7px;
   top: 7px;
   width: 14px;
 }
 
 .close-button:hover {
-  background-image: url('chrome://theme/IDR_WEB_UI_CLOSE_HOVER');
+  background-image: url('chrome://theme/IDR_CLOSE_DIALOG_H');
 }
 
 .close-button:active {
-  background-image: url('chrome://theme/IDR_WEB_UI_CLOSE_PRESSED');
+  background-image: url('chrome://theme/IDR_CLOSE_DIALOG_P');
 }
 
 html[dir=rtl] .close-button {
   left: 10px;
   right: auto;
 }
 
 #bubble {
   -webkit-transition: 250ms opacity;
 }
@@ skipping 105 matching lines @@
   width: 100%;
 }
 
 .background-initial {
   opacity: 0;
 }
 
 .background-final {
   opacity: 1;
 }