Add constants for material colors and shadows

sky/examples/fn/widgets/drawer.dart

Index: sky/examples/fn/widgets/drawer.dart
diff --git a/sky/examples/fn/widgets/drawer.dart b/sky/examples/fn/widgets/drawer.dart
index 26edbb2f07d6b6ade11d5f86552f51ab5d3f07f2..ab7277d64e0c86dccbffa16418d39b13aca55c85 100644
--- a/sky/examples/fn/widgets/drawer.dart
+++ b/sky/examples/fn/widgets/drawer.dart
@@ -103,7 +103,7 @@ class Drawer extends Component {
     left: 0;
     bottom: 0;
     right: 0;
-    box-shadow: 0 10px 20px rgba(0,0,0,0.19), 0 6px 6px rgba(0,0,0,0.23);'''
+    box-shadpw: ${Shadow[3]};'''
   );
 
   static Style _maskStyle = new Style('''
@@ -117,7 +117,7 @@ class Drawer extends Component {
   );
 
   static Style _contentStyle = new Style('''
-    background-color: #FAFAFA;
+    background-color: ${Grey[50]};
     will-change: transform;
     position: absolute;
     z-index: 3;