Add PostCSS to CSS stack

[tylersticka]

In my Feeling Sassy Again article, I mentioned how I thought that Sass was best for proprietary/compiled features while PostCSS was best at browser compatibility and automated/robot stuff.

I think in my ideal world, the CSS stack for this would be something like this...

• We include a browserslist file.
• PostCSS is configured to run Preset Env and Autoprefixer, both of which will change their behavior based on browserslist.
• Files ending in .css are processed by just PostCSS.
• Files ending in .scss are processed by Sass, then by PostCSS.

This will give us:

• The ability to automatically polyfill CSS features based on a project's target browsers.
• The ability to opt in to proprietary Sass stuff when we want to, ignore it if/when we don't need it.

That said, the latter point isn't super important to me. If supporting Sass-less compilation means that importing gets confusing, then that may not be a reasonable trade-off.

[Paul-Hebert]

That makes sense to me! I'm definitely open to that approach!