Ok but you still need to use css and stuff to design the div container. It would be nice if there is control for that. Just set its initial state and voila.
However thank you for the answer .. it makes sense but as mentioned would be nice if you have such control.
Well that IS the radpanelbar essentially...I mean they can't create a specific control for every conceivable situation. That's where their templatability comes in handy. My solution requires MINIMAL Css (this isn't a complex thing to make), I think you're overthinking how hard it is to replicate :) You could literally use firebug to copy that pages CSS and tweak to make it your own. Actually theirs could use some IMPROVEMENTS...if you notice the div kindof expands as it drops down so the controls dont really move much (almost as if they're stationary and the panel moves down to make them visible). I'd say it would look better if they existed above the top of the page and the entire div slid down, not expanded in (if that makes sense).
You could use a custom skin on the radpanelbar, and put your controls inside a template for when it expands...but you'd be downloading a all of scripts and CSS for that control where you really just need a few styles (like a float on the button, and setting it to the top of the screen) and a line or two of jQuery (again, packaged with the telerik suite)
It's literally a hidden div better served by some basic jQuery, but give the RadPanelbar a try if you want...that's the closest thing they have to match it out of the box...just hook into some of the client events for when it expands and collapses.