title: Check scrolling with CSS
body: <p>I am trying to create a pure 100% CSS (no jQuery) "Back to Top" button but I would like the button to show only if the visitor scrolls down the page.</p>
  
  <p>Is it possible to check that with CSS somehow? So if visitor scrolled down a bit show the "Back to Top" button.</p>
  
  <p>Thanks!</p>