gatsby-plugin-dark-mode

A Gatsby plugin which handles some of the details of implementing a dark mode theme.

It provides:

Browser code for toggling and persisting the theme (from Dan Abramov's overreacted.io implementation)
Automatic use of a dark mode theme (via the prefers-color-scheme CSS media query) if you've configured your system to use dark colour themes when available.
A React component for implementing theme toggling UI in your site.

Install

npm install gatsby-plugin-dark-mode

// gatsby-config.js

module.exports = {
  plugins: ['gatsby-plugin-dark-mode'],
}

How to use

Implement theme toggling UI

The plugin module exports a ThemeToggler component which takes a children render prop, providing the current theme name and a toggleTheme function to change the theme.

Here's an example of using ThemeToggler with a checkbox to toggle the theme:

import React from 'react'
import { ThemeToggler } from 'gatsby-plugin-dark-mode'

class MyComponent extends React.Component {
  render() {
    return (
      <ThemeToggler>
        {({ theme, toggleTheme }) => (
          <label>
            <input
              type="checkbox"
              onChange={e => toggleTheme(e.target.checked ? 'dark' : 'light')}
              checked={theme === 'dark'}
            />{' '}
            Dark mode
          </label>
        )}
      </ThemeToggler>
    )
  }
}

The toggled theme will be persisted across visits in localStorage.theme.

Implement theming

The default theme names are 'light' and 'dark' - the plugin adds the current theme name to the <body> element's className, so you can use global styles to implement theming.

A nice option is to use CSS variables like so:

/* global.css */

body {
  --bg: white;
  --textNormal: #222;
  --textTitle: #222;
  --textLink: blue;
  --hr: hsla(0, 0%, 0%, 0.2);

  background-color: var(--bg);
}

body.dark {
  -webkit-font-smoothing: antialiased;

  --bg: darkslategray;
  --textNormal: rgba(255, 255, 255, 0.88);
  --textTitle: white;
  --textLink: yellow;
  --hr: hsla(0, 0%, 100%, 0.2);
}

You can then use these variables in your site's components...

class Layout extends React.Component {
  render() {
    return (
      <div
        style={{
          backgroundColor: 'var(--bg)',
          color: 'var(--textNormal)',
          transition: 'color 0.2s ease-out, background 0.2s ease-out',
        }}
      >
        ...
      </div>
    )
  }
}

...and in your Typography config if you're using gatsby-plugin-typography, which is included in the Gatsby Starter Blog:

// typography.js

import './global.css'

import Typography from 'typography'
import Wordpress2016 from 'typography-theme-wordpress-2016'

Wordpress2016.overrideThemeStyles = () => ({
  a: {
    color: 'var(--textLink)',
  },
  // gatsby-remark-autolink-headers - don't underline when hidden
  'a.anchor': {
    boxShadow: 'none',
  },
  // gatsby-remark-autolink-headers - use theme colours for the link icon
  'a.anchor svg[aria-hidden="true"]': {
    stroke: 'var(--textLink)',
  },
  hr: {
    background: 'var(--hr)',
  },
})

Acknowledgements

The theme detecting/switching/persistence code and the suggested theming implementation are entirely from the implementation of overreacted.io by Dan Abramov - I'm just publishing them as a plugin to make them easier to use in my own blog, and for reuse by others.