code: function cssnext (tagName, css) {
    // A small hack: it passes :scope as :root to PostCSS.
    // This make it easy to use css variables inside tags.
    css = css.replace(/:scope/g, ':root')
    css = postcss([postcssCssnext]).process(css).css
    css = css.replace(/:root/g, ':scope')
    return css
  }
docs: Transforms new CSS specs into more compatible CSS