CSS.supports polyfill is missing

[ertugrulcetin]

It would be nice to have CSS.supports polyfill, yesterday our production went down due to this polyfill :) Here is the souce code: https://github.com/termi/CSS.supports

[MoritzLoewenstein]

I am trying to implement this, there seem to be a few different, possibly outdated polyfills out there:

1. https://github.com/termi/CSS.supports
2. https://github.com/vevlins/CSS.supports (fork of 1.)
3. https://gist.github.com/codler/03a0995195aa2859465f
4. Complete Replacement for CSS.supports and [at]supports in css https://github.com/kjarmicki/fq-polyfill
   The third one is by far the shortest, I will check for spec compliance.

Optimal would be a polyfill which also utilizes earlier implementation (see here ) when needed.

[ertugrulcetin]

@JakeChampion when will this be available on http://polyfill.io ?

[JakeChampion]

PR to update polyfill.io -- polyfillpolyfill/polyfill-service#2211