How is this widget working?

Question

https://scontent-waw1-1.xx.fbcdn.net/v/t34.0-12/18518720_1276620929123347_1493324457_n.png?oh=411dddd50dc512f532f527d65973dd89&oe=591E6963

There is a clock, hour and minute selector that works awesome, but in totally ununderstandable way ( for me). What can this actually be? 2 drop down lists nested in some container? If yes how does it happen that numbers become partially transparent and then vanish completely? And is there any kind of ready widget that lets u select something scrolled from upper or lower level to te center(selecting) point? something else than drop list? Any even rough idea would be great because i could keep googling about it :P

Answer 1

The link is expired.
You can inspect element or view Page Source if it's a web page to see the code.