//open inventory window
private void OpenInventory()
{
var inventory = new InventoryWindow();
inventory.TopLevel = false;
inventory.Visible = true;
inventory.FormBorderStyle = FormBorderStyle.None;
inventory.Dock = DockStyle.Fill;
tabPage2.Controls.Add(inventory);
}
private void Stock_Click(object sender, EventArgs e)
{
var inventoryWindow = new InventoryWindow();
inventoryWindow.ShowDialog();
}