Pull up the Command Palette (Tools > Command Palette). Type "repository" and select Package Control: Add Repository. Paste in the github url (https://github.com/subhaze/CSS-sublime-package
) and press return. Go back to the Command Palette, type "install", then select Package Control: Install Package. Begin typing the name of the package, CSS Sublime Package, and it should show up in the drop down menu. Then to test it, open up a CSS file or create a new file and change the syntax to CSS (View > Syntax > CSS) and it should work as intended.