protected override void OnRender(DrawingContext drawingContext)
        {
            if (this.Margin == WindowsUtilities.ZeroThickness)
            {
                return;
            }

            // Draw background.
            var backgroundRect = new Rect(this.Margin.Left, this.Margin.Top,
                this.ActualWidth - this.Margin.Left - this.Margin.Right,
                this.ActualHeight - this.Margin.Top - this.Margin.Bottom
            );

            // Draw border shadows.
            var leftRect = new Rect(0, this.Margin.Top,
                this.Margin.Left, this.ActualHeight - this.Margin.Top - this.Margin.Bottom
            );
            drawingContext.DrawRectangle(leftBrush, null, leftRect);

            var topRect = new Rect(this.Margin.Left, 0,
                this.ActualWidth - this.Margin.Left - this.Margin.Right, this.Margin.Top
            );
            drawingContext.DrawRectangle(topBrush, null, topRect);

            var rightRect = new Rect(this.ActualWidth - this.Margin.Right,
                this.Margin.Top, this.Margin.Right,
                this.ActualHeight - this.Margin.Top - this.Margin.Bottom
            );
            drawingContext.DrawRectangle(rightBrush, null, rightRect);

            var bottomRect = new Rect(this.Margin.Left,
                this.ActualHeight - this.Margin.Bottom,
                this.ActualWidth - this.Margin.Left - this.Margin.Top,
                this.Margin.Bottom
            );
            drawingContext.DrawRectangle(bottomBrush, null, bottomRect);

            var topLeftRect = new Rect(0, 0, this.Margin.Left, this.Margin.Top);
            drawingContext.DrawRectangle(topLeftBrush, null, topLeftRect);

            var topRightRect = new Rect(this.ActualWidth - this.Margin.Left, 0,
                this.Margin.Right, this.Margin.Top
            );
            drawingContext.DrawRectangle(topRightBrush, null, topRightRect);

            var bottomLeftRect = new Rect(0, this.ActualHeight - this.Margin.Bottom,
                this.Margin.Left, this.Margin.Bottom
            );
            drawingContext.DrawRectangle(bottomLeftBrush, null, bottomLeftRect);

            var bottomRightRect = new Rect(this.ActualWidth - this.Margin.Right,
                this.ActualHeight - this.Margin.Bottom,
                this.Margin.Right, this.Margin.Bottom
            );
            drawingContext.DrawRectangle(bottomRightBrush, null, bottomRightRect);
        }