atom-cssnano 
Minify CSS with cssnano.
Install
apm install cssnanoUsage
Open the Command Palette and enter cssnano. Alternately, use either the
context menus or ctrl + alt + o on your keyboard.
You can customise the output in the settings menu.
Contributing
Pull requests are welcome. If you add functionality, then please add unit tests to cover it.
License
MIT © Ben Briggs