Reply To: Possible to toggle a div display based on what is currently viewable on screen?

[Merri]

Probably the only way you can do it in CSS only: http://codepen.io/Merri/pen/pAmce

So you work with z-index to hide the fixed element behind scrolling elements.

If you want to get different behavior then JavaScript is the only way. CSS provides no mechanism to know scrolling position or if element is viewable on the screen/viewport.