top/bottom shadow should now go away in gaia signin screen.

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

 /* Copyright (c) 2011 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.
  */
 
 body {
   background: -webkit-gradient(radial, center center, 0, center center, 400,
               from(#fefefe), to(#efefef));
@@ skipping 18 matching lines @@
   position: relative;
   width: 640px;
 }
 
 #security-info a,
 #eula a {
   color: #006668;
   text-decoration: none;
 }
 
-hr.topshadow {
+hr.shadow {

[xiyuan, 2011/08/05 23:40:17]

Do we want "-webkit-transition: opacity .2s ease-in-out;" here?

[achuithb, 2011/08/05 23:43:15]

I should've written an explanation. The transition is overridden by the
body.login-display hr selector below.

   -webkit-mask: -webkit-linear-gradient(left, rgba(0,0,0,0),
                                         black 50%, rgba(0,0,0,0));
   -webkit-mask-clip: padding-box;
+  border: none;
+  opacity: 0.3
+}
+
+hr.top {
   background: -webkit-linear-gradient(rgba(0,0,0,0.3), rgba(0,0,0,0.0));
-  border: none;
   border-top: 1px solid rgba(0,0,0,0.5);
   height: 4px;
-  opacity: 0.3;
 }
 
-hr.bottomshadow {
-  -webkit-mask: -webkit-linear-gradient(left, rgba(0,0,0,0),
-                                        black 50%, rgba(0,0,0,0));
-  -webkit-mask-clip: padding-box;
+hr.bottom {
   background: -webkit-linear-gradient(bottom, top,
                                       rgba(0,0,0,0.2)), rgba(0,0,0,0.0));
-  border: none;
   border-bottom: 1px solid rgba(0,0,0,0.5);
   height: 2px;
-  opacity: 0.3;
 }
 
 #header {
   background: url('chrome://theme/IDR_PRODUCT_LOGO_64') left center no-repeat;
   background-size: 48px;
   color: #737373;
   display: -webkit-box;
   font-size: 20px;
   height: 48px;
   line-height: 48px;
@@ skipping 398 matching lines @@
   margin: 0;
   padding: 0;
 }
 
 body.login-display #oobe {
   -webkit-margin-start: -550px;
   width: 1100px;
 }
 
 body.login-display #oobe hr {
   -webkit-transition: all .8s ease;

[achuithb, 2011/08/05 23:43:15]

This transition overrides the shadow transition

[xiyuan, 2011/08/05 23:47:03]

Yep, you are right.

   width: 1100px;  /* Necessary. Otherwise hr shrinks to 0 first when switching
                      from 640px to full width. */
 }
 
 body.login-display #oobe.signin hr,
 body.login-display #oobe.gaia-signin hr {
-  width: 640px;
+  opacity: 0;
 }
 
 body.login-display #inner-container {
   height: 262px;
   padding: 0;
   width: 1100px;
 }
 
 body.login-display .step {
   left: 230px;  /* (1100px - 640px) / 2, make it center in oobe div */
@@ skipping 31 matching lines @@
 #version-labels {
   -webkit-transition: all .5s linear;
   bottom: 10px;
   color: #999;
   font-size: 11px;
   left: 10px;
   opacity: 1.0;
   position: absolute;
   text-shadow: 0 1px 1px #fff;
 }