src/language-css/printer-postcss.js/isKeyframeAtRuleKeywords
function isKeyframeAtRuleKeywords(path, value) {
  const atRuleAncestorNode = getAncestorNode(path, "css-atrule");
  return (
    atRuleAncestorNode &&
    atRuleAncestorNode.name &&
    atRuleAncestorNode.name.toLowerCase().endsWith("keyframes") &&
    ["from", "to"].indexOf(value.toLowerCase()) !== -1
  );
}