It's data-[offset]-(viewport-anchor)-[element-anchor]
and not data-[offset]-(element-anchor)-[viewport-anchor]
.
For example your first element has two keyframes both relative to the bottom of the viewport. But it never even gets close to the bottom!
Correct:
<div class="imp-text-one" data--25-top-bottom="opacity: 0;" data--25-bottom-bottom="opacity: 1">This is important text</div>
<div class="placeholder"></div>
<div class="imp-text-two" data--25-top-bottom="opacity: 0;" data--25-bottom-bottom="opacity: 1">This is also important text</div>
<div class="placeholder"></div>
<div class="imp-text-three" data--25-top-bottom="opacity: 0;" data--25-bottom-bottom:"opacity: 1">
This is VERY important text</div>
Edit: You need to add a proper doctype, e.g. <!DOCTYPE html>
. Otherwise browsers switch to quirks mode, which skrollr doesn't handle.