C#

public partial class BaseControl : UserControl
{
    public BaseControl()
    {
        InitializeComponent();
        SetStyle(ControlStyles.DoubleBuffer | ControlStyles.UserPaint | ControlStyles.AllPaintingInWmPaint | ControlStyles.EnableNotifyMessage, true);
    }
    protected override void OnPaint(PaintEventArgs e)
    {
        if (this.BackgroundImage == null)
        {
            Rectangle rect = new Rectangle(0, 0, Width, Height);
            LinearGradientBrush b = new LinearGradientBrush(rect, Color.White, Color.Blue, 90);
            GraphicsPath path = GraphicsPathUtility.GetRoundRectPath(rect, 10);
            e.Graphics.FillPath(b, path);
        }
        base.OnPaint(e);
     }
}

#region Utility Classes
public class GraphicsPathUtility
{
    private GraphicsPathUtility()
    {
    }
    public static GraphicsPath GetRoundRectPath(RectangleF rect, float radius)
    {
        return GetRoundRectPath(rect.X, rect.Y, rect.Width, rect.Height, radius);
    }
    public static GraphicsPath GetRoundRectPath(float X, float Y, float width, float height, float radius)
    {
        GraphicsPath gp = new GraphicsPath();
        gp.AddLine(X + radius, Y, X + width - (radius * 2), Y); //
        gp.AddArc(X + width - (radius * 2), Y, radius * 2, radius * 2, 270, 90);//
        gp.AddLine(X + width, Y + radius, X + width, Y + height - (radius * 2));
        gp.AddArc(X + width - (radius * 2), Y + height - (radius * 2), radius * 2, radius * 2, 0, 90);
        gp.AddLine(X + width - (radius * 2), Y + height, X + radius, Y + height);
        gp.AddArc(X, Y + height - (radius * 2), radius * 2, radius * 2, 90, 90);
        gp.AddLine(X, Y + height - (radius * 2), X, Y + radius);
        gp.AddArc(X, Y, radius * 2, radius * 2, 180, 90);
        gp.CloseFigure();
        return gp;
    }
}
#endregion