Dock all forms inside parent control

Hello.

I am using RadRibbonBar (Main Form). I have multiple buttons in ribbon. Each button has different forms. I want dock them inside its Main Form on click. here is an example in below screenshot. I am unable to achieve the requirement.

Please note: The child form should dock exactly below the ribbon form. and also, the cross button (child form close button) should be present right after the tab (Child form name).

Please attach a zip file with a source code.

Thanks