Removing unused CSS with Purgecss/UnCSS

[knowler]

@jasonbaciulis

cssnanoConfig inside postcss.config.js is set to remove all comments and that prevents whitelisting directly within SCSS files. So just set to use default preset:

const cssnanoConfig = { preset: ['default'] };

Now just mark comments as important /*! purgecss ignore */ and cssnano will leave them be.

Just made a pull request (#2078) that will fix this issue when (and if) merged.

You will still need to leave the comment as important, but other tools like Autoprefixer recognize that this is necessary when using Sass or Less. It works without the important comment in normal (Post)CSS.