function supportedKeyframes(key) {
  // Keyframes is already prefixed. e.g. key = '@-webkit-keyframes a'
  if (key[1] === '-') return key; // No need to prefix IE/Edge. Older browsers will ignore unsupported rules.
  // https://caniuse.com/#search=keyframes

  if (prefix.js === 'ms') return key;
  return "@" + prefix.css + "keyframes" + key.substr(10);
}
Test if a keyframe at-rule should be prefixed or not

@param {String} vendor prefix string for the current browser.
@return {String}
@api public