private void SigninBtn_Click(object sender, EventArgs e)
{
this.Hide();
SigninForm signin_form = new SigninForm();
signin_form.ShowDialog();
this.Close();
}
private void SignoutBtn_Click(object sender, EventArgs e)
{
// Thuc hien dang xuat
this.Hide();
SigninForm signin_form = new SigninForm();
signin_form.ShowDialog();
Variable_Helper.clear_all(); // Xoa tat ca bien chung
this.Close();
}// Nut sign out