- You could have mentioned relative-mode, as this would make the keyframes independent from where the header starts and how high it is. With relative mode you can resize the header and add a top margin without needing to adjust the keyframes (0 and 500).
- In the last paragraph (mobile) you're including the IE plugin without mentioning what it does (and you say it's the mobile version).
- The IE plugin adds support for rgb and hsl colors and patches querySelector to at least support ID selectors (for data-anchor-target)
But the relative mode stuff would make a great follow up I guess.
Thanks for that Alexander (and thank you karadayi-13 for your input) :)