Why I can't change the border of my Button

Hi,

First I am sorry for my english I am learning.

I have this code

`
public class Whisp : Button
{
public static WhispList whispList = new WhispList ();

    private static int globalID = 0;

    public int ID
    {
        get;
        private set;
    }
    public Whisp (string Texte)
    {
        ID = globalID;
        globalID++;
        this.BorderWidth = 10;
        this.BorderColor = Color.Red;
        this.FontSize = 20;
        Text = string.Format ("{0} {1}", Texte, ID);
        Whisp.whispList.Add (this);
    }
}

`

But i don't know why I still don't have a red border.

Thanks for your help.``````````