@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 visa 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)
  • 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 JavaScript

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.

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:

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.

With Parcel

Add the following to your .parcelrc:

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

Benchmarks

$ node bench.js bootstrap-4.css 
cssnano: 542.956ms
159636 bytes

esbuild: 17.411ms
160332 bytes

parcel-css: 4.602ms
143154 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