Please see url: http://www.mdvip.com/.
Scroll down the page and see how the top section of the page completely collapses and displays the second section of the page. I think this is pure CSS with no .js but I can't really tell anything by the code (flexbox maybe??). Anyway, I would love to know how to do this if anyone is familiar with the technique used here. If you know of a tutorial you can point me to that would be great. :)