Theme UI

Build consistent, themeable React apps based on constraint-based design principles | Built with Emotion + Styled System + MDX + Typography.js

https://theme-ui.com

Built for white-labels, themes, and other applications where customizing colors, typography, and layout are treated as first-class citizens and based on the System UI Theme Specification, Theme UI is intended to work in a variety of applications, libraries, and other UI components. Colors, typography, and layout styles derived from customizable scales and design tokens, help you build UI rooted in constraint-based design principles.

• Styled system without creating components
• First class support for the css prop
• Style MDX content with a simple, expressive API
• Use Typography.js themes
• Works with virtually any UI component library
• Works with existing Styled System components
• Quick mobile-first responsive styles
• Built-in support for dark modes
• Primitive page layout components
• Plugin for use in Gatsby sites and themes
• Define your own design tokens
• Built with the System UI Theme Specification for interoperability
• Keep styles isolated with Emotion

Getting Started

npm i theme-ui @emotion/core @mdx-js/react

Any styles in your app can reference values from the global theme object. To provide the theme in context, wrap your application with the ThemeProvider component and pass in a custom theme object.

// basic usage
import React from 'react'
import { ThemeProvider } from 'theme-ui'
import theme from './theme'

export default props => (
  <ThemeProvider theme={theme}>{props.children}</ThemeProvider>
)

The theme object follows the System UI Theme Specification, which lets you define custom color palettes, typographic scales, fonts, and more. Read more about theming.

// example theme.js
export default {
  fonts: {
    body: 'system-ui, sans-serif',
    heading: '"Avenir Next", sans-serif',
    monospace: 'Menlo, monospace',
  },
  colors: {
    text: '#000',
    background: '#fff',
    primary: '#33e',
  },
}

sx prop

The sx prop works similarly to Emotion's css prop, accepting style objects to add CSS directly to an element in JSX, but includes extra theme-aware functionality. Using the sx prop for styles means that certain properties can reference values defined in your theme object. This is intended to make keeping styles consistent throughout your app the easy thing to do.

The sx prop only works in modules that have defined a custom pragma at the top of the file, which replaces the default React.createElement function. This means you can control which modules in your application opt into this feature without the need for a Babel plugin or additional configuration.

/** @jsx jsx */
import { jsx } from 'theme-ui'

export default props => (
  <div
    sx={{
      fontWeight: 'bold',
      fontSize: 4, // picks up value from `theme.fontSizes[4]`
      color: 'primary', // picks up value from `theme.colors.primary`
    }}>
    Hello
  </div>
)

Under the hood, this uses the @styled-system/css utility and Emotion's custom JSX pragma implementation. Read more about how the custom pragma works.

Responsive styles

The sx prop also supports using arrays as values to change properties responsively with a mobile-first approach. This API originated in Styled System and is intended as a terser syntax for applying responsive styles across a singular dimension.

/** @jsx jsx */
import { jsx } from 'theme-ui'

export default props => (
  <div
    sx={{
      // applies width 100% to all viewport widths,
      // width 50% above the first breakpoint,
      // and 25% above the next breakpoint
      width: ['100%', '50%', '25%'],
    }}
  />
)

Documentation

• Theming
• The sx Prop
• Layout
• Color Modes
• Styled
• MDX Components
• Theme Spec
• Gatsby Plugin
• API

MIT License