Fixed @kekekeks notes.

src/Perspex.Controls/Shapes/Line.cs

@@ -19,9 +19,9 @@ namespace Perspex.Controls.Shapes
         private Point _startPoint;
         private Point _endPoint;
 
-        public Line()
+        static Line()
         {
-            StrokeThickness = 1;
+            StrokeThicknessProperty.OverrideDefaultValue<Line>(1);
         }
 
         public Point StartPoint

src/Perspex.Controls/Shapes/Polyline.cs

@@ -12,9 +12,9 @@ namespace Perspex.Controls.Shapes
         public static readonly PerspexProperty<IList<Point>> PointsProperty =
             PerspexProperty.Register<Polyline, IList<Point>>("Points");
 
-        public Polyline()
+        static Polyline()
         {
-            StrokeThickness = 1; // Default Thickness
+            StrokeThicknessProperty.OverrideDefaultValue<Polyline>(1);
         }
 
         public IList<Point> Points