private void btn_sanpham_Click(object sender, EventArgs e)
{
this.Hide();
frmSach sach = new frmSach();
sach.ShowDialog();
}
private void quảnLýKhoSáchToolStripMenuItem_Click(object sender, EventArgs e)
{
this.Hide();
frmSach sach = new frmSach();
sach.ShowDialog();
}