message: Allow empty call to CSS plugin
diff: import textLoader from "../loaders/text.js";
  import { postcss, postcssImport, postcssNesting } from "../deps/postcss.js";
  -export default function ({ postcssPlugins = [] }) {
  +export default function (options = {}) {
  + const { postcssPlugins = [postcssNesting()] } = options;
  return (site) => {
  const runner = postcss([
  postcssImport({
  path: site.src("_includes"),
  }),
  - postcssNesting(),
  ...postcssPlugins,
  ]);
  