It will take your CSS file, apply minification, encoding and encypting and finally injects this unreadable crap into tailored JS library (also obfuscated).
The result you will get is this tailored (unique) library, containing obfuscated CSS. Just include it in the place of the original CSS.
What it does not:
It will not speed up displaying of your web.
It will not hide CSS rules in inspector (developer's tools) - but it don't mind, attacker will probably not copy all stuff by one rule.
Notice:
At-rules (@charset, @media, ...) are not supported yet, except @import. Move them into other, non-obfuscated files.