Contents cache demo

Issue: 3091

Question/Feature: Critical CSS when extract CSS flag is true on Nuxt Generate

I saw vue cli 3 has now got some config options that would be nice to have on nuxt.
Particularly I saw this plugin
https://github.com/anthonygore/vue-cli-plugin-critical/blob/master/README.md

Which would be nice to have particularly for static sites

_{This feature request is available on Nuxt.js community (#c2676)}