5. Combine with Other CSS Processing.

Combining with other CSS post-processes. Using theme engine with CSS preprocessor:

css-dev --> tmp-css  ------ o ---------- o ----------------- > css 
                            |            |
                    autoprefixer     CSS preprocessor

Set 'target' to temporary place( folder ). Apply autoprefixer or/and preprocessors over the result of theme engine and then save in production folder.

Using just CSS:

css-dev --> css

If you are using pure CSS you are save to write results directly in production folder.