Post-Processing CSS is the technical workflow of using automated tools to transform modern CSS into a production-ready format that is optimized for performance and cross-browser compatibility. Tools like PostCSS, Autoprefixer, and SASS allow developers to use advanced features like nesting and variables during development. During the "build" phase, the post-processor "minifies" the code, adds necessary browser prefixes (like -webkit or -moz), and purges unused styles. For a high-end WordPress site, this ensures that the visitor only downloads the exact CSS needed to render the page, reducing the "Unused CSS" warnings often found in PageSpeed reports. In an era where site speed is a direct ranking factor, post-processing is a mandatory step for any professional developer building custom themes or blocks.
Glossary entry