PostCSS Preset Env lets you transform modern CSS so most browsers can understand, determining the polyfills you need based on the browsers you want. It's essentially like Babel Preset-Env for CSS - a bundle of CSS polyfills and polyfills applied at compile time.

Core Functionality: PostCSS Preset Env takes support data from MDN and Can I Use, and determines from a browserslist whether transformations are needed. It also packs Autoprefixer within and shares the list with it, so prefixes are automatically handled.

Key Features:

1. Stage-Based Feature Support

• The stage option determines which CSS features to polyfill, based upon their stability in the process of becoming implemented web standards, ranging from stage 0 (experimental) through 4 (stable).

• Without any configuration, PostCSS Preset Env enables Stage 2 features and supports all browsers.

2. Feature Selection

• The features option enables or disables specific polyfills by ID, allowing you to enable experimental features while using more stable stages.

• Access to hundreds of modern CSS features like nesting rules, custom properties, color functions, and more

3. Browser Targeting

• The browsers option determines which polyfills are required based upon the browsers you're supporting, using standard browserslist configuration.

• Automatically omits polyfills for features already supported by target browsers

4. Built-in Autoprefixer

• PostCSS Preset Env includes autoprefixer and the browsers option is passed to it automatically.

• Eliminates need for separate autoprefixer configuration

5. Standards Compliance

• Only packs plugins that enable features acknowledged by the World Wide Web Consortium (W3C) which will then be implemented by browsers later.

• Helps developers write standards-compliant future CSS today

Available Features Include:

• CSS nesting rules

• Custom properties and media queries

• Color functions (like alpha(), color-mod())

• Logical properties

• :any-link, :blank pseudo-classes

• Break properties

• All-property reset

• And many more modern CSS features

Benefits:

• Write modern CSS syntax today without browser compatibility concerns

• Easier migration to native CSS features as browser support improves

• More stable codebase compared to non-standard CSS preprocessors

• Interactive playground available for testing features

• Configurable preservation of original CSS for progressive enhancement

Target Users: Front-end developers wanting to use cutting-edge CSS features while maintaining broad browser support, similar to how Babel enables modern JavaScript usage.