@parcel/css

A CSS parser, transformer, and minifier written in Rust.

Features

• Extremely fast – Parsing and minifying large files is completed in milliseconds, often with significantly smaller output than other tools. See benchmarks below.
• Typed property values – many other CSS parsers treat property values as an untyped series of tokens. This means that each transformer that wants to do something with these values must interpret them itself, leading to duplicate work and inconsistencies. @parcel/css parses all values using the grammar from the CSS specification, and exposes a specific value type for each property.
• Browser-grade parser – @parcel/css is built on the cssparser and selectors crates created by Mozilla and used by Firefox and Servo. These provide a solid general purpose CSS-parsing foundation on top of which @parcel/css implements support for all specific CSS rules and properties.
• Minification – One of the main purposes of @parcel/css is to minify CSS to make it smaller. This includes many optimizations including:
  • Combining longhand properties into shorthands where possible.
  • Merging adjacent rules with the same selectors or declarations when it is safe to do so.
  • Combining CSS transforms into a single matrix or vice versa when smaller.
  • Removing vendor prefixes that are not needed, based on the provided browser targets.
  • Reducing calc() expressions where possible.
  • Converting colors to shorter hex notation where possible.
  • Minifying gradients.
  • Minifying CSS grid templates.
  • Normalizing property value order.
  • Removing default property sub-values which will be inferred by browsers.
  • Many micro-optimizations, e.g. converting to shorter units, removing unnecessary quotation marks, etc.
• Vendor prefixing – @parcel/css accepts a list of browser targets, and automatically adds (and removes) vendor prefixes.
• Syntax lowering – @parcel/css parses modern CSS syntax, and generates more compatible output where needed, based on browser targets.
  • CSS Nesting (draft spec)
  • Custom media queries (draft spec)
  • Logical properties
  • CSS Level 4 Color syntax
  • Space separated components in rgb and hsl functions
  • Hex with alpha syntax
  • hwb() color syntax
  • Percent syntax for opacity
  • Double position gradient stops (e.g. red 40% 80%)
  • clamp() function
  • Alignment shorthands (e.g. place-items)
  • Two-value overflow shorthand
  • Media query range syntax (e.g. @media (width <= 100px) or @media (100px < width < 500px))
  • Multi-value display property (e.g. inline flex)
• CSS modules – @parcel/css supports compiling a subset of CSS modules features.
  • Locally scoped class and id selectors
  • Locally scoped custom identifiers, e.g. @keyframes names, grid lines/areas, @counter-style names, etc.
  • :local() and :global() selectors
  • The composes property

Documentation

@parcel/css can be used from Parcel, as a standalone library from JavaScript or Rust, or wrapped as a plugin within any other tool.

From Node

See the TypeScript definitions for full API docs.

Here is a simple example that compiles the input CSS for Safari 13.2, and minifies the output.

```js const css = require('@parcel/css');

let {code, map} = css.transform({ filename: 'style.css', code: Buffer.from('.foo { color: red }'), minify: true, sourceMap: true, targets: { // Semver versions are represented using a single 24-bit number, with one component per byte. // e.g. to represent 13.2.0, the following could be used. safari: (13 << 16) | (2 << 8) } }); ```

You can also convert the results of running browserslist into targets which can be passed to @parcel/css:

```js const browserslist = require('browserslist'); const css = require('@parcel/css');

let targets = css.browserslistToTargets(browserslist('>= 0.25%')); ```

From Rust

See the Rust API docs on docs.rs. More docs and examples are coming soon. For now, start with the StyleSheet API.

With Parcel

Add the following to your .parcelrc:

json { "extends": "@parcel/config-default", "transformers": { "*.css": ["@parcel/transformer-css-experimental"] }, "optimizers": { "*.css": ["@parcel/optimizer-css"] } }

You should also add a browserslist property to your package.json, which defines the target browsers that your CSS will be compiled for.

While Parcel CSS handles the most commonly used PostCSS plugins like autoprefixer, postcss-preset-env, and CSS modules, you may still need PostCSS for more custom plugins like TailwindCSS. If that's the case, just add @parcel/transformer-postcss before @parcel/transformer-css-experimental, and your PostCSS config will be picked up automatically. You can remove the plugins listed above from your PostCSS config, and they'll be handled by Parcel CSS.

You can also configure Parcel CSS in the package.json in the root of your project. Currently, three options are supported: drafts, which can be used to enable CSS nesting and custom media queries, pseudoClasses, which allows replacing some pseudo classes like :focus-visible with normal classes that can be applied via JavaScript (e.g. polyfills), and cssModules, which enables CSS modules globally rather than only for files ending in .module.css.

json { "@parcel/transformer-css": { "cssModules": true, "drafts": { "nesting": true, "customMedia": true }, "pseudoClasses": { "focusVisible": "focus-ring" } } }

From Deno or in browser

The @parcel/css-wasm package can be used in Deno or directly in browsers. This uses a WebAssembly build of Parcel CSS. Use TextEncoder and TextDecoder convert code from a string to a typed array and back.

```js import init, {transform} from 'https://unpkg.com/@parcel/css-wasm';

await init();

let {code, map} = transform({ filename: 'style.css', code: new TextEncoder().encode('.foo { color: red }'), minify: true, });

console.log(new TextDecoder().decode(code)); ```

Benchmarks

``` $ node bench.js bootstrap-4.css cssnano: 542.879ms 159636 bytes

esbuild: 16.839ms 160332 bytes

parcel-css: 4.345ms 143121 bytes

$ node bench.js animate.css cssnano: 283.105ms 71723 bytes

esbuild: 11.858ms 72183 bytes

parcel-css: 1.973ms 23666 bytes

$ node bench.js tailwind.css cssnano: 2.198s 1925626 bytes

esbuild: 107.668ms 1961642 bytes

parcel-css: 43.368ms 1824130 bytes ```