BACK BUTTON + APP BAR

Runtime/material/app_bar.cs

+namespace Unity.UIWidgets.material {
+    public class app_bar {
+        
+    }
+}

Runtime/material/back_button.cs

+using Unity.UIWidgets.foundation;
+using Unity.UIWidgets.ui;
+using Unity.UIWidgets.widgets;
+
+namespace Unity.UIWidgets.material {
+    public class BackButtonIcon : StatelessWidget {
+        public BackButtonIcon(
+            Key key = null) : base(key: key) {
+        }
+
+        static IconData _getIconData() {
+            return Icons.arrow_back;
+        }
+
+        public override Widget build(BuildContext context) {
+            return new Icon(_getIconData());
+        }
+    }
+
+    public class BackButton : StatelessWidget {
+        public BackButton(
+            Key key = null,
+            Color color = null) : base(key: key) {
+            this.color = color;
+        }
+
+        public readonly Color color;
+
+        public override Widget build(BuildContext context) {
+            return new IconButton(
+                icon: new BackButtonIcon(),
+                color: this.color,
+                onPressed: () => { Navigator.maybePop(context); });
+        }
+    }
+
+    public class CloseButton : StatelessWidget {
+        public CloseButton(
+            Key key = null) : base(key: key) {
+        }
+        
+        public override Widget build(BuildContext context) {
+            return new IconButton(
+                icon: new Icon(Icons.close),
+                onPressed: () => { Navigator.maybePop(context); });
+        }
+    }
+}

Runtime/material/bottom_app_bar.cs

+namespace Unity.UIWidgets.material {
+    public class bottom_app_bar {
+        
+    }
+}

Runtime/widgets/perferred_size.cs

+using System.Drawing;
+using Unity.UIWidgets.foundation;
+
+namespace Unity.UIWidgets.widgets {
+    
+    public interface PreferredSizeWidget {
+        Size preferredSize { get; }
+    }
+
+
+    public class PreferredSize : StatelessWidget, PreferredSizeWidget {
+        public PreferredSize(
+            Key key = null,
+            Widget child = null,
+            Size? preferredSize = null) : base(key: key) {
+            D.assert(child != null);
+            D.assert(preferredSize != null);
+            this.child = child;
+            this.preferredSize = preferredSize ?? Size.Empty;
+        }
+
+        public readonly Widget child;
+
+        public Size preferredSize { get; }
+
+        public override Widget build(BuildContext context) {
+            return this.child;
+        }
+    }
+}