We can't use block when we have constrained space anymore. Use Flex instead.

sky/sdk/example/demo_launcher/lib/main.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 'package:sky/mojo/activity.dart' as activity;
 import 'package:sky/mojo/asset_bundle.dart';
 import 'package:sky/painting/box_painter.dart';
 import 'package:sky/theme/colors.dart' as colors;
 import 'package:sky/theme/typography.dart' as typography;
 import 'package:sky/widgets/basic.dart';
@@ skipping 128 matching lines @@
         child: new Card(
           child: new Flex([
             new Flexible(
               child: new Stack([
                 new Container(
                   decoration: demo.decoration,
                   child: new Container()
                 ),
                 new Container(
                   margin: const EdgeDims.all(24.0),
-                  child: new Block([
-                    new Text(demo.name, style: demo.textTheme.title),
-                    new Text(demo.description, style: demo.textTheme.subhead)
-                  ])
+                  child: new Flex([
+                      new Text(demo.name, style: demo.textTheme.title),
+                      new Flexible(
+                        child: new Text(demo.description, style: demo.textTheme.subhead)
+                      )
+                    ],
+                    direction: FlexDirection.vertical,
+                    alignItems: FlexAlignItems.start)
                 )
               ])
             ),
           ], direction: FlexDirection.vertical)
         )
       )
     );
   }
 
   Widget build() {
@@ skipping 23 matching lines @@
           )
         )
       )
     );
   }
 }
 
 void main() {
   runApp(new SkyHome());
 }