Re-work MaterialComponent

sky/framework/components/button.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 'button_base.dart';
+import 'material.dart';
 
 class Button extends ButtonBase {
   static final Style _style = new Style('''
     transform: translateX(0);
     display: inline-flex;
     border-radius: 4px;
     justify-content: center;
     align-items: center;
     border: 1px solid blue;
     -webkit-user-select: none;
@@ skipping 10 matching lines @@
     -webkit-user-select: none;
     margin: 5px;
     background-color: orange;'''
   );
 
   Node content;
 
   Button({ Object key, this.content }) : super(key: key);
 
   Node build() {
-    return new Container(
+    return new Material(
       style: highlight ? _highlightStyle : _style,
-      children: [super.build(), content]
+      children: [content]
     );
   }
 }