Update Button to be made of Material

sky/framework/components/drawer_header.dart

 // 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 '../fn.dart';
 import '../theme/colors.dart';
 
 class DrawerHeader extends Component {
   static final Style _style = new Style('''
     display: flex;
@@ skipping 15 matching lines @@
     font-family: 'Roboto Medium', 'Helvetica';
     color: #212121;'''
   );
 
   List<Node> children;
 
   DrawerHeader({ Object key, this.children }) : super(key: key);
 
   Node build() {
     return new Container(
-      style: _style,
+      styles: [_style],
       children: [
         new Container(
           key: 'Spacer',
-          style: _spacerStyle
+          styles: [_spacerStyle]
         ),
         new Container(
           key: 'Label',
-          style: _labelStyle,
+          styles: [_labelStyle],
           children: children
         )
       ]
     );
   }
 }