chrome/browser/resources/chromeos/login/screen_account_picker.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.
 */

#account-picker {
  -webkit-box-align: center;
  -webkit-box-orient: vertical;
  -webkit-box-pack: center;
  /*
   * Account picker has .step class but should be
   * fully transparent and w/o border.
   */
  background: transparent;
  box-shadow: none;
  display: -webkit-box;
  left: 0;
  margin: 0;
  padding: 0;
}

#multiple-signin-banner {
  background-color: rgba(0, 0, 0, 0.75);
  border-radius: 4px;
  color: whitesmoke;
  display: none;
  font-size: 15px;
  padding: 20px;
}

html[screen=user-adding] #multiple-signin-banner {
  display: block;
}