src/language-css/loc.js/getValueRootOffset
function getValueRootOffset(node) {
  return (
    node.source.startOffset +
    (typeof node.prop === "string" ? node.prop.length : 0) +
    (node.type === "css-atrule" && typeof node.name === "string"
      ? 1 + node.name.length + getLeadingWhitespaceLength(node.raws.afterName)
      : 0) +
    (node.type !== "css-atrule" &&
    node.raws &&
    typeof node.raws.between === "string"
      ? node.raws.between.length
      : 0)
  );
}