private void btnKunde_Click(object sender, EventArgs e)
{
if (frmKun != null)
{
frmKun.BringToFront();
}
else
{
btnKunde.BackColor = Color.White;
btnKunde.ForeColor = btnBackColor;
frmKun = new frmKunde();
frmKun.Text = "Kundenverwaltung";
frmKun.Show();
}
}