Add close button to the supervised user pages.

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

 /* Copyright 2014 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 Locally managed user creation flow screen.
  */
 
 #supervised-user-creation {
   height: 609px; /* Same size as GAIA sign in screen.*/
   padding: 0 0;  /* Some screens have elements right next to borders. */
@@ skipping 531 matching lines @@
   margin-left: -22px;
   margin-top: -22px;
   position: absolute;
   top: 50%;
   width: 44px;
 }
 
 .camera.live:not(.online) .supervised-user-creation-image-stream-area .spinner {
   display: block;
 }
+
+.custom-gaia-button {
+  background: transparent none;
+  background-position: center;
+  background-repeat: no-repeat;
+  border-radius: 50%;
+  height: 24px;
+  position: absolute;
+  top: 10px;
+  width: 24px;
+  z-index: 1;
+}
+
+.custom-gaia-button:hover {
+  cursor: pointer;
+}
+
+.custom-gaia-button:focus {
+  background: rgba(0,0,0,.16);
+  background-position: center;
+  background-repeat: no-repeat;
+  opacity: 0.75;
+}
+
+ /* Even more specificity than button.custom-appearance:focus:focus */
+.custom-gaia-button:focus:focus:focus {
+   border-color: transparent;
+}
+
+.custom-gaia-button:active {
+  background: rgba(0,0,0,.12);
+  background-position: center;
+  background-repeat: no-repeat;
+  opacity: 1.0;
+}
+
+#supervised-user-creation-close-button-item {
+  background-image: url(chrome://theme/IDR_LOGIN_CLOSE_BUTTTON_ON_WHITE);
+  right: 10px;
+}
+
+html[dir=rtl] #supervised-user-creation-close-button-item {
+  left: 10px;
+  right: auto;
+}
+
+#supervised-user-creation-close-button-item:disabled {
+  background-image: url(chrome://theme/IDR_LOGIN_CLOSE_BUTTTON_MASKED);
+}