I am trying to implement an custom form in Piranha CMS 2.2.4. The form renders to a new page, showing only the form. My goal is the that the form renders juist like a normal content page.

My code snippets:
Index.cmshtml

```
@inherits Piranha.WebPages.SinglePage<Piranha.Models.PageModel>
@{
  var msg = "";

  if (IsPost)
  {
    var order = new Order()
    {
      Item = Request["Item"],
      Quantity = Request["Quantity"]
    };
    order.Save();
    msg = "Your order is saved!";
  }
}

@if (!String.IsNullOrEmpty(msg))
{
  <p>@msg</p>
}
<div>
  <form method="post">
    <input name="Item" />
    <input name="Quantity" />
    <button type="submit">Let's buy it!</button>
  </form>
</div> 

```

Order.cs:

```
public class Order
{
  public String Item { get; set; }
  public String Quantity { get; set; }

  public Order()
  {
  }

  public void Save()
  {
  }
}

```

What I am missing?

Any help is appreciated