I have been spending some time getting postcss into my workflow. I started using it with gulp in my build process. The best thing about postcss is this plugin echo system.
http://postcss.parts/ - A searchable list of plugins
Below are the few plugins that I used in my last few projects. https://github.com/postcss/postcss-simple-vars - PostCSS Simple Variables https://github.com/postcss/postcss-mixins - PostCSS Mixins https://github.com/antyakushev/postcss-for - https://github.com/antyakushev/postcss-for