Check out postcss-cssnext on GitHub or try it in your browser
PostCSS-cssnext is a PostCSS plugin that helps you to use the latest CSS syntax today. It transforms new CSS specs into more compatible CSS so you don't need to wait for browser support. You can literally write future-proof CSS and forget old preprocessor specific syntax.
filterproperty (svg fallback)
:notpseudo-class (to l.3)
::pseudo syntax (
system-uifont-family (font-family fallback)
Prior to 2015, CSS was frustrating by not having any specification for features we were looking for. No variables, no math, no color manipulation & no customization. Things are going to change soon since a lot of work has been made by the W3C to write new specs to make our life easier. With cssnext, you can start using some new features today!
In a near future, browsers will implement new CSS specifications. As time passes, cssnext will remove some transformations that won't be necessary anymore. And maybe one day, you will be able to completely remove cssnext from your workflow without touching your CSS.
cssnext uses PostCSS
a way faster CSS parser.
It's a good competitor to libsass, a bit faster than LESS and Stylecow, and way faster than Myth or original Ruby Sass.