@jsenv/plugin-minification/src/css/css_minification.js

import { urlToFileSystemPath } from "@jsenv/urls";

export const minifyCss = async (cssUrlInfo) => {
  const { transform } = await import("lightningcss");

  const targets = runtimeCompatToTargets(cssUrlInfo.context.runtimeCompat);
  const { code, map } = transform({
    filename: urlToFileSystemPath(cssUrlInfo.originalUrl),
    code: Buffer.from(cssUrlInfo.content),
    targets,
    minify: true,
  });
  return {
    content: String(code),
    sourcemap: map,
  };
};

const runtimeCompatToTargets = (runtimeCompat) => {
  const targets = {};
  ["chrome", "firefox", "ie", "opera", "safari"].forEach((runtimeName) => {
    const version = runtimeCompat[runtimeName];
    if (version) {
      targets[runtimeName] = versionToBits(version);
    }
  });
  return targets;
};

const versionToBits = (version) => {
  const [major, minor = 0, patch = 0] = version
    .split("-")[0]
    .split(".")
    .map((v) => parseInt(v, 10));
  return (major << 16) | (minor << 8) | patch;
};