kiosk: Network connectivity test during launch.

chrome/browser/resources/chromeos/login/screen_error_message.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.
  */
 
 #error-message {
   width: 650px;
 }
 
 .show-with-ui-state-update,
@@ skipping 73 matching lines @@
 }
 
 #offline-network-control {
   -webkit-align-items: center;
   display: -webkit-flex;
 }
 
 .offline-network-list-label {
   -webkit-margin-end: 10px;
 }
+
+.button-spacer {
+  -webkit-box-flex: 1;
+}