Suggest an editImprove this articleRefine the answer for “How does PostCSS process CSS files?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**PostCSS** processes CSS step by step, going through three main stages: parsing → transformation → generating the result. **Key point:** the whole process is built around plugins that change CSS in sequence; PostCSS itself changes nothing, the plugins do all the work.Shown above the full answer for quick recall.Answer (EN)ImagePostCSS processes CSS step by step, going through three main stages: **parsing → transformation → generating the result**. The whole process is built around plugins that change the CSS in sequence. --- ### **1) Parsing** PostCSS reads the source CSS and turns it into an **Abstract Syntax Tree (AST)**: a data structure where every selector, property, value and media query is a node in the tree. This is needed so plugins can work with a structured representation of the code instead of with strings. --- ### **2) Transformation (the most important part)** The CSS AST is passed through the chain of connected plugins. Each plugin analyzes the tree and modifies it for its own task: - Autoprefixer: adds vendor prefixes by changing properties - cssnano: removes unnecessary nodes and minifies - postcss-preset-env: converts modern features (for example, nesting) into compatible code - PurgeCSS: removes unnecessary rules - and so on PostCSS itself changes nothing: **the plugins do everything**. --- ### **3) Generating the final CSS** Once the plugins have finished their transformations, PostCSS turns the AST back into a string: a new CSS file that goes to production. --- ### **Process diagram** ```javascript Source CSS ↓ Parsing (AST) ↓ PostCSS plugins (chain) ↓ Generated CSS (clean, optimized, cross-browser) ``` --- ### **The main idea** PostCSS is not a preprocessor that "extends the syntax"; it is an **engine for transforming CSS that already exists, using plugins**. That is why it became the standard for bundlers (Vite, Webpack, Parcel) in production.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.