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    3.0.9 • Public • Published



    TypeScript and Flow definitions for CSS, generated by data from MDN. It provides autocompletion and type checking for CSS properties and values.


    import * as CSS from 'csstype';
    const style: CSS.Properties = {
      colour: 'white', // Type error on property
      textAlign: 'middle', // Type error on value


    // @flow strict
    import * as CSS from 'csstype';
    const style: CSS.Properties<> = {
      colour: 'white', // Type error on property
      textAlign: 'middle', // Type error on value

    Further examples below will be in TypeScript!

    Getting started

    $ npm install csstype

    Table of content

    Style types

    Properties are categorized in different uses and in several technical variations to provide typings that suits as many as possible.

    Default Hyphen Fallback HyphenFallback
    All Properties PropertiesHyphen PropertiesFallback PropertiesHyphenFallback
    Standard StandardProperties StandardPropertiesHyphen StandardPropertiesFallback StandardPropertiesHyphenFallback
    Vendor VendorProperties VendorPropertiesHyphen VendorPropertiesFallback VendorPropertiesHyphenFallback
    Obsolete ObsoleteProperties ObsoletePropertiesHyphen ObsoletePropertiesFallback ObsoletePropertiesHyphenFallback
    Svg SvgProperties SvgPropertiesHyphen SvgPropertiesFallback SvgPropertiesHyphenFallback


    • All - Includes Standard, Vendor, Obsolete and Svg
    • Standard - Current properties and extends subcategories StandardLonghand and StandardShorthand (e.g. StandardShorthandProperties)
    • Vendor - Vendor prefixed properties and extends subcategories VendorLonghand and VendorShorthand (e.g. VendorShorthandProperties)
    • Obsolete - Removed or deprecated properties
    • Svg - SVG-specific properties


    • Default - JavaScript (camel) cased property names
    • Hyphen - CSS (kebab) cased property names
    • Fallback - Also accepts array of values e.g. string | string[]

    At-rule types

    At-rule interfaces with descriptors.

    TypeScript: These will be found in the AtRule namespace, e.g. AtRule.Viewport.
    Flow: These will be prefixed with AtRule$, e.g. AtRule$Viewport.

    Default Hyphen Fallback HyphenFallback
    @counter-style CounterStyle CounterStyleHyphen CounterStyleFallback CounterStyleHyphenFallback
    @font-face FontFace FontFaceHyphen FontFaceFallback FontFaceHyphenFallback
    @viewport Viewport ViewportHyphen ViewportFallback ViewportHyphenFallback

    Pseudo types

    String literals of pseudo classes and pseudo elements

    • Pseudos


      • AdvancedPseudos

        Function-like pseudos e.g. :not(:first-child). The string literal contains the value excluding the parenthesis: :not. These are separated because they require an argument that results in infinite number of variations.

      • SimplePseudos

        Plain pseudos e.g. :hover that can only be one variation.


    All interfaces has two optional generic argument to define length and time: CSS.Properties<TLength = string | 0, TTime = string>

    • Length is the first generic parameter and defaults to string | 0 because 0 is the only length where the unit identifier is optional. You can specify this, e.g. string | number, for platforms and libraries that accepts any numeric value as length with a specific unit.
      const style: CSS.Properties<string | number> = {
        width: 100,
    • Time is the second generic argument and defaults to string. You can specify this, e.g. string | number, for platforms and libraries that accepts any numeric value as length with a specific unit.
      const style: CSS.Properties<string | number, number> = {
        transitionDuration: 1000,


    import * as CSS from 'csstype';
    const style: CSS.Properties = {
      width: '10px',
      margin: '1em',

    In some cases, like for CSS-in-JS libraries, an array of values is a way to provide fallback values in CSS. Using CSS.PropertiesFallback instead of CSS.Properties will add the possibility to use any property value as an array of values.

    import * as CSS from 'csstype';
    const style: CSS.PropertiesFallback = {
      display: ['-webkit-flex', 'flex'],
      color: 'white',

    There's even string literals for pseudo selectors and elements.

    import * as CSS from 'csstype';
    const pseudos: { [P in CSS.SimplePseudos]?: CSS.Properties } = {
      ':hover': {
        display: 'flex',

    Hyphen cased (kebab cased) properties are provided in CSS.PropertiesHyphen and CSS.PropertiesHyphenFallback. It's not not added by default in CSS.Properties. To allow both of them, you can simply extend with CSS.PropertiesHyphen or/and CSS.PropertiesHyphenFallback.

    import * as CSS from 'csstype';
    interface Style extends CSS.Properties, CSS.PropertiesHyphen {}
    const style: Style = {
      'flex-grow': 1,
      'flex-shrink': 0,
      'font-weight': 'normal',
      backgroundColor: 'white',

    Adding type checked CSS properties to a HTMLElement.

    import * as CSS from 'csstype';
    const style: CSS.Properties = {
      color: 'red',
      margin: '1em',
    let button = document.createElement('button');
    Object.assign(button.style, style);

    What should I do when I get type errors?

    The goal is to have as perfect types as possible and we're trying to do our best. But with CSS Custom Properties, the CSS specification changing frequently and vendors implementing their own specifications with new releases sometimes causes type errors even if it should work. Here's some steps you could take to get it fixed:

    If you're using CSS Custom Properties you can step directly to step 3.

    1. First of all, make sure you're doing it right. A type error could also indicate that you're not 😉

      • Some CSS specs that some vendors has implemented could have been officially rejected or haven't yet received any official acceptance and are therefor not included
      • If you're using TypeScript, type widening could be the reason you get Type 'string' is not assignable to... errors
    2. Have a look in issues to see if an issue already has been filed. If not, create a new one. To help us out, please refer to any information you have found.

    3. Fix the issue locally with TypeScript (Flow further down):

      • The recommended way is to use module augmentation. Here's a few examples:

        // My css.d.ts file
        import * as CSS from 'csstype';
        declare module 'csstype' {
          interface Properties {
            // Add a missing property
            WebkitRocketLauncher?: string;
            // Add a CSS Custom Property
            '--theme-color'?: 'black' | 'white';
            // ...or allow any other property
            [index: string]: any;
      • The alternative way is to use type assertion. Here's a few examples:

        const style: CSS.Properties = {
          // Add a missing property
          ['WebkitRocketLauncher' as any]: 'launching',
          // Add a CSS Custom Property
          ['--theme-color' as any]: 'black',

      Fix the issue locally with Flow:

      • Use type assertion. Here's a few examples:

        const style: $Exact<CSS.Properties<*>> = {
          // Add a missing property
          [('WebkitRocketLauncher': any)]: 'launching',
          // Add a CSS Custom Property
          [('--theme-color': any)]: 'black',

    Version 3.0

    • All property types are exposed with namespace
      TypeScript: Property.AlignContent (was AlignContentProperty before)
      Flow: Property$AlignContent
    • All at-rules are exposed with namespace
      TypeScript: AtRule.FontFace (was FontFace before)
      Flow: AtRule$FontFace
    • Data types are NOT exposed
      E.g. Color and Box. Because the generation of data types may suddenly be removed or renamed.
    • TypeScript hack for autocompletion
      Uses (string & {}) for literal string unions and (number & {}) for literal number unions (related issue). Utilize PropertyValue<T> to unpack types from e.g. (string & {}) to string.
    • New generic for time
      Read more on the "Generics" section.
    • Flow types improvements
      Flow Strict enabled and exact types are used.


    Never modify index.d.ts and index.js.flow directly. They are generated automatically and committed so that we can easily follow any change it results in. Therefor it's important that you run $ git config merge.ours.driver true after you've forked and cloned. That setting prevents merge conflicts when doing rebase.


    • npm run build Generates typings and type checks them
    • npm run watch Runs build on each save
    • npm run test Runs the tests
    • npm run lazy Type checks, lints and formats everything


    npm i csstype

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    • anders.ekdahl
    • faddee