Add a box-shadow to the app-bar per material design

sky/examples/stocks/stocks.sky

 <!--
 // Copyright 2015 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.
 -->
 <import src="/sky/framework/sky-drawer.sky" />
 <import src="/sky/framework/sky-element.sky" />
 <import src="/sky/framework/sky-scrollable.sky" />
 <import src="stock.sky" as='view'/>
 <import src='companylist.sky' as='model'/>
@@ skipping 12 matching lines @@
       position: absolute;
       z-index: 1;
       top: 0;
       left: 0;
       bottom: 0;
       right: 0;
     }
     sky-toolbar {
       display: flex;
       align-items: center;
-      background-color: #526E9C;
+      background-color: #3F51B5;
       color: white;
       height: 56px;
+      box-shadow: 0px 4px 4px grey;
     }
     #menu {
       display: flex;
       justify-content: center;
       align-items: center;
       width: 24px;
       height: 24px;
       padding: 7px;
       margin: 0 8px;
       background-color: papayawhip;
@@ skipping 52 matching lines @@
   }
 
   void _handleMenuClick(_) {
     _drawer.toggle();
   }
 }
 
 _init(script) => register(script, Stocks);
 </script>
 </sky-element>