private void openGUI(Player player) {
        Inventory inv = Bukkit.createInventory(null, 27, ChatColor.DARK_AQUA + "LevelUp Confirmation");

        ItemStack yes = new ItemStack(Material.EMERALD_BLOCK);
        ItemMeta yesMeta = yes.getItemMeta();
        ItemStack no = new ItemStack(Material.EMERALD_BLOCK);
        ItemMeta noMeta = no.getItemMeta();

        yesMeta.setDisplayName(ChatColor.GREEN + "Click me to confirm");
        yes.setItemMeta(yesMeta);

        noMeta.setDisplayName(ChatColor.RED + "Click me to cancel");
        no.setItemMeta(noMeta);

        inv.setItem(1, yes);
        inv.setItem(2, yes);
        inv.setItem(3, yes);
        inv.setItem(10, yes);
        inv.setItem(11, yes);
        inv.setItem(12, yes);
        inv.setItem(19, yes);
        inv.setItem(20, yes);
        inv.setItem(21, yes);
        inv.setItem(9, no);
        inv.setItem(8, no);
        inv.setItem(7, no);
        inv.setItem(18, no);
        inv.setItem(17, no);
        inv.setItem(16, no);
        inv.setItem(27, no);
        inv.setItem(26, no);
        inv.setItem(25, no);