Styles are compiled using SASS. We use autoprefixer, so you don't worry about writing browser prefixes of any kind, it's all done automatically with support for the latest 2 major versions of every browser. You'll need Node and Gulp installed globally. After that, from the theme's root directory:
$ yarn install $ yarn dev
Now you can edit
/assets/scss/ files, which will be compiled to
zip Gulp task packages the theme files into
dist/<theme-name>.zip, which you can then upload to the blog of your choice.
$ yarn zip