only just got around to this scroll animations css only, trying some more complex ones at the moment, not sure how good this is yet
Oh that looks nifty, nice work 
All css only - ok this does not work in all browsers yet, in Firefox it needs to be turned on, so just for fun, or you could use. I will delete tomorrow.
project- elementsapp://downloadDocument/4jqScQyOW1xC
ok more complex took me a while to put in keyframes, left and right ok, the center animation not so good, 3 dropzones, need to work on option to add own paths
Those are additions are pretty cool, keep up the good work 