diff --git a/src/codelabs/layout-basics.md b/src/codelabs/layout-basics.md
index fd4ec1e968..632bf24c5f 100644
--- a/src/codelabs/layout-basics.md
+++ b/src/codelabs/layout-basics.md
@@ -93,11 +93,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -123,7 +123,7 @@ Future<void> main() async {
 
   final columns = controller.widgetList(find.byType(Column));
 
-  if (columns.length == 0) {
+  if (columns.isEmpty) {
     _result(false, ['The Row contains three BlueBox widgets and lays them out horizontally.']);
     return;
   }
@@ -235,11 +235,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -263,7 +263,7 @@ Future<void> main() async {
 
   final rows = controller.widgetList(find.byType(Row));
 
-  if (rows.length == 0) {
+  if (rows.isEmpty) {
     _result(false, ['Couldn\'t find Row!']);
     return;
   }
@@ -377,11 +377,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -404,7 +404,7 @@ Future<void> main() async {
 
   final rows = controller.widgetList(find.byType(Row));
 
-  if (rows.length == 0) {
+  if (rows.isEmpty) {
     _result(false, ['Couldn\'t find a Row!']);
     return;
   }
@@ -551,11 +551,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -579,7 +579,7 @@ Future<void> main() async {
 
   final rows = controller.widgetList(find.byType(Row));
 
-  if (rows.length == 0) {
+  if (rows.isEmpty) {
     _result(false, ['Couldn\'t find a Row!']);
     return;
   }
@@ -712,11 +712,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -740,7 +740,7 @@ Future<void> main() async {
 
   final rows = controller.widgetList(find.byType(Row));
 
-  if (rows.length == 0) {
+  if (rows.isEmpty) {
     _result(false, ['Couldn\'t find a Row!']);
     return;
   }
@@ -870,11 +870,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -898,7 +898,7 @@ Future<void> main() async {
 
   final rows = controller.widgetList(find.byType(Row));
 
-  if (rows.length == 0) {
+  if (rows.isEmpty) {
     _result(false, ['Couldn\'t find a Row!']);
     return;
   }
@@ -1028,11 +1028,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -1056,7 +1056,7 @@ Future<void> main() async {
 
   final rows = controller.widgetList(find.byType(Row));
 
-  if (rows.length == 0) {
+  if (rows.isEmpty) {
     _result(false, ['Couldn\'t find a Row!']);
     return;
   }
@@ -1160,11 +1160,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -1188,7 +1188,7 @@ Future<void> main() async {
 
   final rows = controller.widgetList(find.byType(Row));
 
-  if (rows.length == 0) {
+  if (rows.isEmpty) {
     _result(false, ['Couldn\'t find a Row!']);
     return;
   }
@@ -1301,11 +1301,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -1329,7 +1329,7 @@ Future<void> main() async {
 
   final rows = controller.widgetList(find.byType(Row));
 
-  if (rows.length == 0) {
+  if (rows.isEmpty) {
     _result(false, ['Couldn\'t find a Row!']);
     return;
   }
@@ -1469,11 +1469,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -1497,7 +1497,7 @@ Future<void> main() async {
 
   final rows = controller.widgetList(find.byType(Row));
 
-  if (rows.length == 0) {
+  if (rows.isEmpty) {
     _result(false, ['Couldn\'t find a Row!']);
     return;
   }
@@ -1616,11 +1616,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -1644,7 +1644,7 @@ Future<void> main() async {
 
   final rows = controller.widgetList(find.byType(Row));
 
-  if (rows.length == 0) {
+  if (rows.isEmpty) {
     _result(false, ['Couldn\'t find a Row!']);
     return;
   }
@@ -1741,11 +1741,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -1769,7 +1769,7 @@ Future<void> main() async {
 
   final rows = controller.widgetList(find.byType(Row));
 
-  if (rows.length == 0) {
+  if (rows.isEmpty) {
     _result(false, ['Couldn\'t find a Row!']);
     return;
   }
@@ -1858,11 +1858,11 @@ class MyApp extends StatelessWidget {
     return Directionality(
       textDirection: TextDirection.ltr,
       child: Container(
-        color: Color(0xffeeeeee),
+        color: const Color(0xffeeeeee),
         child: Center(
           child: Container(
             child: MyWidget(),
-            color: Color(0xffcccccc),
+            color: const Color(0xffcccccc),
           ),
         ),
       ),
@@ -1886,7 +1886,7 @@ Future<void> main() async {
 
   final rows = controller.widgetList(find.byType(Row));
 
-  if (rows.length == 0) {
+  if (rows.isEmpty) {
     _result(false, ['Couldn\'t find a Row!']);
     return;
   }
@@ -1997,7 +1997,7 @@ class MyWidget extends StatelessWidget {
           'Flutter McFlutter', 
           style: Theme.of(context).textTheme.headline5,
         ),
-        Text('Experienced App Developer'),
+        const Text('Experienced App Developer'),
       ],
     );
   }
@@ -2010,8 +2010,8 @@ class MyApp extends StatelessWidget {
     return MaterialApp(
       debugShowCheckedModeBanner: false,
       theme: ThemeData(
-        scaffoldBackgroundColor: Color(0xffeeeeee),
-        textTheme: TextTheme(
+        scaffoldBackgroundColor: const Color(0xffeeeeee),
+        textTheme: const TextTheme(
           bodyText2: TextStyle(
             fontSize: 16,
           ),
@@ -2023,9 +2023,9 @@ class MyApp extends StatelessWidget {
           child: Center(
             child: Container(
               decoration: BoxDecoration(
-                color: Color(0xffffffff),
+                color: const Color(0xffffffff),
                 border: Border.all(),
-                boxShadow: [
+                boxShadow: const [
                   BoxShadow(
                     blurRadius: 10,
                     color: Color(0x80000000),
@@ -2160,7 +2160,7 @@ class MyWidget extends StatelessWidget {
           'Flutter McFlutter',
           style: Theme.of(context).textTheme.headline5,
         ),
-        Text('Experienced App Developer'),
+        const Text('Experienced App Developer'),
       ],
     );
   }
@@ -2176,8 +2176,8 @@ class MyWidget extends StatelessWidget {
   Widget build(BuildContext context) {
     return Row(
       children: [
-        Padding(
-          padding: const EdgeInsets.all(8.0),
+        const Padding(
+          padding: EdgeInsets.all(8.0),
           child: Icon(Icons.account_circle, size: 50),
         ),
         Column(
@@ -2188,7 +2188,7 @@ class MyWidget extends StatelessWidget {
               'Flutter McFlutter',
               style: Theme.of(context).textTheme.headline5,
             ),
-            Text('Experienced App Developer'),
+            const Text('Experienced App Developer'),
           ],
         ),
       ],
@@ -2203,8 +2203,8 @@ class MyApp extends StatelessWidget {
     return MaterialApp(
       debugShowCheckedModeBanner: false,
       theme: ThemeData(
-        scaffoldBackgroundColor: Color(0xffeeeeee),
-        textTheme: TextTheme(
+        scaffoldBackgroundColor: const Color(0xffeeeeee),
+        textTheme: const TextTheme(
           bodyText2: TextStyle(
             fontSize: 16,
           ),
@@ -2216,9 +2216,9 @@ class MyApp extends StatelessWidget {
           child: Center(
             child: Container(
               decoration: BoxDecoration(
-                color: Color(0xffffffff),
+                color: const Color(0xffffffff),
                 border: Border.all(),
-                boxShadow: [
+                boxShadow: const [
                   BoxShadow(
                     blurRadius: 10,
                     color: Color(0x80000000),
@@ -2392,8 +2392,8 @@ class MyWidget extends StatelessWidget {
   Widget build(BuildContext context) {
     return Row(
       children: [
-        Padding(
-          padding: const EdgeInsets.all(8.0),
+        const Padding(
+          padding: EdgeInsets.all(8.0),
           child: Icon(Icons.account_circle, size: 50),
         ),
         Column(
@@ -2404,7 +2404,7 @@ class MyWidget extends StatelessWidget {
               'Flutter McFlutter',
               style: Theme.of(context).textTheme.headline5,
             ),
-            Text('Experienced App Developer'),
+            const Text('Experienced App Developer'),
           ],
         ),
       ],
@@ -2426,8 +2426,8 @@ class MyWidget extends StatelessWidget {
       children: [
         Row(
           children: [
-            Padding(
-              padding: const EdgeInsets.all(8.0),
+            const Padding(
+              padding: EdgeInsets.all(8.0),
               child: Icon(Icons.account_circle, size: 50),
             ),
             Column(
@@ -2438,14 +2438,14 @@ class MyWidget extends StatelessWidget {
                   'Flutter McFlutter',
                   style: Theme.of(context).textTheme.headline5,
                 ),
-                Text('Experienced App Developer'),
+                const Text('Experienced App Developer'),
               ],
             ),
           ],
         ),
-        SizedBox(height: 8),
+        const SizedBox(height: 8),
         Row(),
-        SizedBox(height: 16),
+        const SizedBox(height: 16),
         Row(),
       ],
     );
@@ -2459,8 +2459,8 @@ class MyApp extends StatelessWidget {
     return MaterialApp(
       debugShowCheckedModeBanner: false,
       theme: ThemeData(
-        scaffoldBackgroundColor: Color(0xffeeeeee),
-        textTheme: TextTheme(
+        scaffoldBackgroundColor: const Color(0xffeeeeee),
+        textTheme: const TextTheme(
           bodyText2: TextStyle(
             fontSize: 16,
           ),
@@ -2472,9 +2472,9 @@ class MyApp extends StatelessWidget {
           child: Center(
             child: Container(
               decoration: BoxDecoration(
-                color: Color(0xffffffff),
+                color: const Color(0xffffffff),
                 border: Border.all(),
-                boxShadow: [
+                boxShadow: const [
                   BoxShadow(
                     blurRadius: 10,
                     color: Color(0x80000000),
@@ -2681,7 +2681,7 @@ class MyWidget extends StatelessWidget {
       children: [
         Row(
           children: [
-            Padding(
+            const Padding(
               padding: const EdgeInsets.all(8.0),
               child: Icon(Icons.account_circle, size: 50),
             ),
@@ -2693,18 +2693,18 @@ class MyWidget extends StatelessWidget {
                   'Flutter McFlutter',
                   style: Theme.of(context).textTheme.headline5,
                 ),
-                Text('Experienced App Developer'),
+                const Text('Experienced App Developer'),
               ],
             ),
           ],
         ),
-        SizedBox(height: 8),
+        const SizedBox(height: 8),
         Row(
-          children: [],
+          children: const [],
         ),
-        SizedBox(height: 16),
+        const SizedBox(height: 16),
         Row(
-          children: [],
+          children: const [],
         ),
       ],
     );
@@ -2725,8 +2725,8 @@ class MyWidget extends StatelessWidget {
       children: [
         Row(
           children: [
-            Padding(
-              padding: const EdgeInsets.all(8.0),
+            const Padding(
+              padding: EdgeInsets.all(8.0),
               child: Icon(Icons.account_circle, size: 50),
             ),
             Column(
@@ -2737,15 +2737,15 @@ class MyWidget extends StatelessWidget {
                   'Flutter McFlutter',
                   style: Theme.of(context).textTheme.headline5,
                 ),
-                Text('Experienced App Developer'),
+                const Text('Experienced App Developer'),
               ],
             ),
           ],
         ),
-        SizedBox(height: 8),
+        const SizedBox(height: 8),
         Row(
           mainAxisAlignment: MainAxisAlignment.spaceBetween,
-          children: [
+          children: const [
             Text(
               '123 Main Street',
             ),
@@ -2754,9 +2754,9 @@ class MyWidget extends StatelessWidget {
             ),
           ],
         ),
-        SizedBox(height: 16),
+        const SizedBox(height: 16),
         Row(
-          children: [],
+          children: const [],
         ),
       ],
     );
@@ -2770,8 +2770,8 @@ class MyApp extends StatelessWidget {
     return MaterialApp(
       debugShowCheckedModeBanner: false,
       theme: ThemeData(
-        scaffoldBackgroundColor: Color(0xffeeeeee),
-        textTheme: TextTheme(
+        scaffoldBackgroundColor: const Color(0xffeeeeee),
+        textTheme: const TextTheme(
           bodyText2: TextStyle(
             fontSize: 16,
           ),
@@ -2783,9 +2783,9 @@ class MyApp extends StatelessWidget {
           child: Center(
             child: Container(
               decoration: BoxDecoration(
-                color: Color(0xffffffff),
+                color: const Color(0xffffffff),
                 border: Border.all(),
-                boxShadow: [
+                boxShadow: const [
                   BoxShadow(
                     blurRadius: 10,
                     color: Color(0x80000000),
@@ -3012,8 +3012,8 @@ class MyWidget extends StatelessWidget {
       children: [
         Row(
           children: [
-            Padding(
-              padding: const EdgeInsets.all(8.0),
+            const Padding(
+              padding: EdgeInsets.all(8.0),
               child: Icon(Icons.account_circle, size: 50),
             ),
             Column(
@@ -3024,22 +3024,22 @@ class MyWidget extends StatelessWidget {
                   'Flutter McFlutter',
                   style: Theme.of(context).textTheme.headline5,
                 ),
-                Text('Experienced App Developer'),
+                const Text('Experienced App Developer'),
               ],
             ),
           ],
         ),
-        SizedBox(height: 8),
+        const SizedBox(height: 8),
         Row(
           mainAxisAlignment: MainAxisAlignment.spaceBetween,
-          children: [
+          children: const [
             Text('123 Main Street'),
             Text('415-555-0198'),
           ],
         ),
-        SizedBox(height: 16),
+        const SizedBox(height: 16),
         Row(
-          children: [],
+          children: const [],
         ),
       ],
     );
@@ -3060,8 +3060,8 @@ class MyWidget extends StatelessWidget {
       children: [
         Row(
           children: [
-            Padding(
-              padding: const EdgeInsets.all(8.0),
+            const Padding(
+              padding: EdgeInsets.all(8.0),
               child: Icon(Icons.account_circle, size: 50),
             ),
             Column(
@@ -3072,15 +3072,15 @@ class MyWidget extends StatelessWidget {
                   'Flutter McFlutter',
                   style: Theme.of(context).textTheme.headline5,
                 ),
-                Text('Experienced App Developer'),
+                const Text('Experienced App Developer'),
               ],
             ),
           ],
         ),
-        SizedBox(height: 8),
+        const SizedBox(height: 8),
         Row(
           mainAxisAlignment: MainAxisAlignment.spaceBetween,
-          children: [
+          children: const [
             Text(
               '123 Main Street',
             ),
@@ -3089,10 +3089,10 @@ class MyWidget extends StatelessWidget {
             ),
           ],
         ),
-        SizedBox(height: 16),
+        const SizedBox(height: 16),
         Row(
           mainAxisAlignment: MainAxisAlignment.spaceAround,
-          children: [
+          children: const [
             Icon(Icons.accessibility),
             Icon(Icons.timer),
             Icon(Icons.phone_android),
@@ -3111,8 +3111,8 @@ class MyApp extends StatelessWidget {
     return MaterialApp(
       debugShowCheckedModeBanner: false,
       theme: ThemeData(
-        scaffoldBackgroundColor: Color(0xffeeeeee),
-        textTheme: TextTheme(
+        scaffoldBackgroundColor: const Color(0xffeeeeee),
+        textTheme: const TextTheme(
           bodyText2: TextStyle(
             fontSize: 16,
           ),
@@ -3124,9 +3124,9 @@ class MyApp extends StatelessWidget {
           child: Center(
             child: Container(
               decoration: BoxDecoration(
-                color: Color(0xffffffff),
+                color: const Color(0xffffffff),
                 border: Border.all(),
-                boxShadow: [
+                boxShadow: const [
                   BoxShadow(
                     blurRadius: 10,
                     color: Color(0x80000000),