private void button1_Click(object sender, EventArgs e)
        {
            new_vendor f3 = new new_vendor();

            f3.ChangeTab2();
            f3.Show();
            this.Hide();
        }
        private void vendor_list_Click(object sender, EventArgs e)
        {
            new_vendor f2 = new new_vendor();

            f2.ChangeTab();
            f2.Show();
            this.Hide();
        }