Expandable scrolling panel

Hi. 
I got a scrolling panel with a couple of objects on it. 
Its a text then a video and finaly a arrow pointing downwards. 

Now i want the scrolling panel to be filled with more content after the user clicked the arrow. But i can't figure out how to do it or if it's even are possible. 
See picture where i try to explain my idea.  (As you can see i also want the arrow to vanish) 

 

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