Align treeview node expanders properly.

Perspex/Shapes/Shape.cs

@@ -70,22 +70,22 @@ namespace Perspex.Shapes
 
             if (double.IsInfinity(availableSize.Width))
             {
-                desiredX = shapeBounds.Width;
+                desiredX = shapeBounds.Right;
             }
 
             if (double.IsInfinity(availableSize.Height))
             {
-                desiredY = shapeBounds.Height;
+                desiredY = shapeBounds.Bottom;
             }
 
             if (shapeBounds.Width > 0)
             {
-                sx = desiredX / shapeBounds.Width;
+                sx = desiredX / shapeBounds.Right;
             }
 
             if (shapeBounds.Height > 0)
             {
-                sy = desiredY / shapeBounds.Height;
+                sy = desiredY / shapeBounds.Bottom;
             }
 
             if (double.IsInfinity(availableSize.Width))
@@ -123,8 +123,8 @@ namespace Perspex.Shapes
                     break;
             }
 
-            double finalX = (width > 0) ? width : shapeBounds.Width * sx;
-            double finalY = (height > 0) ? height : shapeBounds.Height * sy;
+            double finalX = (width > 0) ? width : shapeBounds.Right * sx;
+            double finalY = (height > 0) ? height : shapeBounds.Bottom * sy;
             return new Size(finalX, finalY);
         }
 

Perspex/Themes/Default/TreeViewItemStyle.cs

@@ -74,10 +74,9 @@ namespace Perspex.Themes.Default
                 Fill = Brushes.Black,
                 Stroke = Brushes.Black,
                 StrokeThickness = 1,
-                Width = 16,
-                Height = 16,
+                Margin = new Thickness(3, 0),
                 VerticalAlignment = Layout.VerticalAlignment.Center,
-                Data = StreamGeometry.Parse("M 4 0 L 8 4 L 4 8 Z"),
+                Data = StreamGeometry.Parse("M 0 2 L 4 6 L 0 10 Z"),
             };
         }
     }

TestApplication/Program.cs

@@ -172,6 +172,7 @@ namespace TestApplication
                         new TabItem
                         {
                             Header = "Lists",
+                            IsSelected = true,
                             Content = new StackPanel
                             {
                                 Orientation = Orientation.Vertical,