private void btn_stok_Click(object sender, EventArgs e)
{
panel_button.Height = btn_stok.Height;
panel_button.Top = btn_stok.Top;
panel_pembelian.Visible = false;
panel_penjualan.Visible = false;
panel_stok.Visible = true;
panel_admin.Visible = false;
panel_report.Visible = false;
panel_supplier.Visible = false;
Stok page_stok = new Stok();
page_stok.TopLevel = false;
panel_stok.Controls.Add(page_stok);
page_stok.Show();
}