How to add logo to Flatty Sticky Header?

[RocketFoot]

I'd like to add my board logo to the sticky header on Flatty theme...so when you scroll down and the main logo becomes covered up, a new, small logo would appear in the sticky header!  I see lots of sites that do this now and I think it would bring a modern element to the forum!

Problem is...I have no idea how to implement this!!