atom-emmet-css-in-js
A companion package to `emmet-atom` which will expand css abbreviations into css-in-js object style
css-in-js support for Emmet
apm install atom-emmet-css-in-js
A companion package to emmet-atom which will expand css abbreviations into css-in-js object style.

This will turn someting like mt0 into marginTop: 0 or jfcsb into justifyContent: 'space-between'.
Check out the emmet docs on css abbreviations to learn more about how to use them.
Keymap
This package does not assign a shortcut by default, you can run Application: Open Your Keymap from the Command Palette add one of your choosing to your keymap.cson:
'atom-text-editor:not([mini])':
'ctrl-w': 'atom-emmet-css-in-js:expand'
Caveats
Note that this package requires emmet-atom to be installed and activated to work.