protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
var image = ApplicationBehaviour.Resources.Images.ArrowDown;
if (!Collapsed) image = ApplicationBehaviour.Resources.Images.ArrowUp;
var imageRect = new Rectangle(8, Height / 2 - image.height / 2, image.width, image.height);
e.Graphics.DrawTexture(image, imageRect);
}