Merging Themes

Sometimes it's useful to split a theme across multiple files, use a preset as the basis for a custom theme, or combine two or more themes together. Since themes are plain JavaScript objects, any merging strategy will work. This guide shows a few common ways to merge themes together.

Using a preset

To use a preset as the basis for a custom theme, it's recommended that you use a deep merge utility. The theme-ui package exports a preconfigured version of the deepmerge package that can be used for this.

// example theme based on preset-future
import future from '@theme-ui/preset-future'
import { merge } from 'theme-ui'
export default merge(future, {
  fonts: {
    body: 'Montserrat, sans-serif',
  },
})

Multiple files

While there is absolutely nothing wrong with keeping an entire theme in a single file, you can split a theme into multiple files (or modules).

// example theme/colors.js
export default {
  text: '#000',
  background: '#fff',
  primary: '#07c',
}

// example theme/fonts.js
export default {
  body: 'system-ui, sans-serif',
  heading: 'Baskerville, Georgia, serif',
  monospace: 'Menlo, monospace',
}

// example theme/index.js
import colors from './colors'
import fonts from './fonts'
export default {
  colors,
  fonts,
}

Merging theme values from multiple files

For the core scales (colors, fontSizes, space, etc), it’s typically simpler to understand a theme when values are defined in one file. However, especially for projects with many styles or variants, you may want to split values that end up as part of one object across multiple files. You can use the same kind of imports combined with the merge utility for this.

// example theme/index.js
import { merge } from 'theme-ui'
import colors from './colors'
import fonts from './fonts'
import textStyles from './styles/text'
import tableStyles from './styles/tables'
import { buttons, forms, links } from './variants'
export default {
  colors,
  fonts,
  styles: merge(textStyles, tableStyles),
  buttons,
  forms,
  links,
}