Remove the |style| parameter from Material

sky/framework/components/button.dart

Index: sky/framework/components/button.dart
diff --git a/sky/framework/components/button.dart b/sky/framework/components/button.dart
index 0a80bbad1ae7f1bf60e9bf84ac04a6f3d0d30d00..bcaa0ad4867fea02e6f3590bb37b0559becd2d4b 100644
--- a/sky/framework/components/button.dart
+++ b/sky/framework/components/button.dart
@@ -25,10 +25,8 @@ class Button extends Component {
   Button({ Object key, this.content, this.level }) : super(key: key);
 
   Node build() {
-    return new Material(
-      style: _style,
-      children: [content],
-      level: level
-    );
+    return new StyleNode(
+      new Material(children: [content], level: level),
+      _style);
   }
 }