Introducing Design System Utils

Your helping hand to enforce your brand & design system styles with any CSS-in-JS solution

Maintaining styling consistency in a web app (or React Native) is often tough. There isn’t a common way to manage shared values and settings. This micro framework aims to standardise your design-system and provide helpful utilities to access it’s information. It’s more than a set of variables in a specific structure, it includes a few functions to access values in your design system much more easily.

Let me run through the basics

You first need to create your design system file, this contains all your global variables that your app will use, think font-sizes, color palette, spacing etc. I usually create a top-level directory named theme or designsystem, and add an index.js inside, like so:

// ./theme/index.js
import DesignSystem from 'design-system-utils'
// your design-system goes here, see below for details
export const myDesignSystem = {...}
export const ds = new DesignSystem(myDesignSystem, {
useModularScale: true,
fontSizeUnit: 'rem',

What is the shape of the design system object?

Below are the mandatory items that your design system should use. Beyond these, you can add anything you like.

type: {
// this should be set as a px value if you have `options.fontSizeUnit` set
// to 'rem' or 'em' so that the lib can convert the values properly
baseFontSize: <string>,
    sizes: {
key: <number | string>,
    // If you're using a modular scale, set it up here
// Use these docs to find out more:
modularscale: {
base: <number | array>, // should be the same as baseFontSize
ratio: <number>,
  // Color palette
// Each object needs to have the same shape
// Each color object needs a `base` value to be the default
// Have as many color objects as you like
colors: {
// Used with `ds.color('colorName')`
colorPalette: {
colorName: {
base: <string>, // base is the default
    // Used with `ds.brand('colorName)`
brand: {
colorName: <string>, // base is the default
  // Breakpoints
// Used with `ds.bp()`
// Keys can be anything you like
// Have as many breakpoints as you like
// Values can be use any unit you like
breakpoints: {
key: <number | string>,
  // Z-index
// Used with `ds.z()`
zIndex: {
key: <number>
  // Spacing
// Used with `ds.spacing()` or ``
spacing: {
scale: <array>[<number | string>, ...],

This is an excerpt from the example design-system. See a more complete example in the example directory.

export const myDesignSystem = {
type: {
baseFontSize: '20px',
    // the values below use modular-scale
sizes: {
xs: -2,
s: -1,
base: 0, // [default] p, h5, h6
m: 1, // h4
l: 2, // h3
xl: 3, // h2
xxl: 4, // h1
    modularscale: {
base: 20,
ratio: 1.5,
    fontFamily: {
'-apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans"',
sans: '"Helvetica Neue", Helvetica, Arial, sans-serif',
serif: 'Georgia, "Times New Roman", Times, serif',
mono: 'Menlo, Monaco, "Courier New", monospace',
    lineHeight: {
headings: 1.1,
    fontWeight: {
normal: 300, // Useful to set here if using anything other than `normal`
bold: 'bold', // Useful to set here when bold webfonts come as 400 font-weight.
headings: 'bold', // instead of browser default, bold

Accessing the design system data in your app

Here I have created a very simple component using the design system and styled-components, you should be able to see how easy it is to pull information from the design system.

// Example uses styled-components
import styled from 'styled-component'
import { ds } from './theme'
export const Box = styled.div`
font-family: ${ds.get('type.fontFamilyBase')}
background-color: ${ds.brand('primary')}
margin: ${} 0


There are two options that can be passed to your design system. These relate to font-sizing.

// Use default options
export const ds = new DesignSystem(myDesignSystem)

// With custom options
export const ds = new DesignSystem(myDesignSystem, {

// converts the `type.sizes` values into modular scale values
useModularScale: true,

// sets the font-size unit when calling fs.fontSize()
fontSizeUnit: 'rem',

API methods

Get any value

The ds.get() function can be used to get any value from the design-system. You can use dot notation to find nested values at any depth.

// with the system setup, as above
ds.get('type.lineHeight.headings') // e.g. 1.1

I have provided a few other helper methods to make retrieving certain values more simple. Most are short-hands for the ds.get() method.


The ds.fontSize() method is a short-hand for the ds.get() method, but with a little extra. It is used to pull values from the type.sizes object.

The type.sizes object’s values can be formatted in a few ways:

  • s: -2 — if a number is used and options.modularscale = true, then ds.fontSize() converts this number to a value on the modular scale.
  • s: '13px'
  • s: '1.4rem'
// define some values
// type.sizes object
sizes: {
xs: -2,
s: -1,
base: 0, // [default] p, h5, h6
m: 1, // h4
l: 2, // h3
xl: 3, // h2
xxl: 4, // h1

// retrieve some values
ds.fs('xl') // `fs()` is a short-hand alias for `fontSize()`
ds.fs('xl', true) // return font-size in px regardless of `option.fontSizeUnit` value
ds.fs(6) // returns font-size of the 6th item on the modular-scale. This will only work if the òptions.modularscale` is `true`

Modular scale
To make use of a modular scale, there are a few things that need to be done:

  • set options.modularscale = true, see above for details on this
  • set your modular scale options in type.modularscale. Design system utils uses modularscale-js to do the conversions.
modularscale: {
base: 20,
ratio: 1.5,

Color palette

There are two possible ways to access color information: through the color palette and the brand colors. The color palette is intended to contain all the colors (and their shades) that your app will use, and the brand palette is the specific colors that your brand uses. Two methods can be used to retrieve the values, these are:

colors: {
// With a color palette like this:
colorPalette: {
bright: {
base: '#F9FAFB',
dark: '#F4F6F8',
darker: '#DFE4E8',
    dark: {
base: '#212B35',
light: '#454F5B',
lighter: '#637381',
  // With a brand palette like this:
brand: {
red: '#e82219',
deeporange: '#ff7200',
orange: '#ff9500',
green: '#c4d000',
teal: '#1aa5c8',
navy: '#0052da',

Get color palette value
The ds.color() function gets values from the colorPalette object. It assumes every color has a base property and other properties for different shades of the same color. This is a short-hand for the ds.get() function.

// Get values like this:
ds.color('bright') // #F9FAFB - the `base` key is the default, so it is not needed
// if you need a color variant, use this
ds.color('bright', 'dark')

Get brand palette value
The ds.brand() function gets values from the colors.brand object. This is a short-hand for the ds.get() function.

// Get brand values like this:
ds.brand('') // it is possible to nest this object as much as you like

Get breakpoint values

The ds.bp() method is a short-hand for the ds.get() method. It can be used to get a breakpoint from the breakpoints object.


Get z-index values

The ds.z() method is a short-hand for the ds.get() method. It can be used to get a breakpoint from the zIndex object.


Get spacing values

The ds.spacing() method returns a value from your spacing.scale array. It takes an index for that array and converts the value to pixels.

// Example scale array
// scale: [0, 8, 16, 24, 32, 40]
ds.spacing(2) // '16px'

Note: can also be used.


The framework currently provides a few calculation functions, multiply and pxTo:

multiply(initial, muliplier)

// ds.multiply(initial, muliplier)
ds.multiply(10, 2) // 20
// you can pass in another value from the system
ds.multiply(ds.get('spacing.baseline'), 2)
// or just use the key from the system
// the initial value will always be run through `parseFloat()`
ds.multiply('spacing.baseline', 2)

pxTo(fontSize, baseFontSize, unit)

Converts px to rem or em

// ds.pxTo(fontSize, baseFontSize, unit)
ds.pxTo(12, 20, 'rem') // 0.6rem
ds.pxTo(12, 20, 'em') // 0.6em

toPx(fontSize, baseFontSize)

Converts rem or em value to px

ds.toPx('1.875rem', 16) // 30px
ds.toPx('1.875em', 16) // 30px

Demo & examples

I created a demo on, it includes examples of using the design-system utils with emotion, styled-components and glamorous. There is also a basic example here.

How do you get it?

You can install it via npm using:

npm install --save design-system-utils

yarn add design-system-utils

How do you contribute?

I am always looking for ways to improve, so welcome any and all feedback. The code is hosted on GitHub at