how to theme your gatsby site

First of all.

The following idea can be applied to all kinds of sites while those use React, you need to know that Gatsby is a React-based open-source framework for creating websites and apps.

The main Idea 💡

We need to know that themes are CSS properties that change when we select a specific theme. eg.

          <button type="button" onClick={handleToggle} style={styles(theme).toggle}>
            { theme === themes.light ? '☽' : '☼' }
          </button>

We will create a dark ☽ and light ☼ theme:

import { createContext, useState } from 'react'

export const themes = {
  light: {
    foreground: 'rebeccapurple',
    background: 'white'
  },
  dark: {
    foreground: 'white',
    background: 'rebeccapurple'
  }
};
export const ThemeContext = createContext();

We need to create also the hook to manage the state of the current theme:

export const useThemes = () => {
  const [mode, setMode] = useState(themes.light);

  const toggleMode = () => { 
    if (mode === themes.light) {
      setMode(themes.dark);
    } else {
      setMode(themes.light);
    }
  };

  return [mode, toggleMode]
};

Please create a context to wrap your app :

import React from "react"
import PropTypes from "prop-types"
import { useStaticQuery, graphql } from "gatsby"

import { ThemeContext, themes, useThemes } from './Context/Theme'

import Header from "./Header"
import "./layout.css"

const Layout = ({ children }) => {

Import and create only one instance of our theme, this is a kind of singleton pattern.

  const [theme, handleToggle ] = useThemes();

  const data = useStaticQuery(graphql`
    query SiteTitleQuery {
      site {
        siteMetadata {
          title
        }
      }
    }
  `)
console.log(theme.foreground);
  return (

    <ThemeContext.Provider value={themes}>
      <Header siteTitle={data.site.siteMetadata.title} handleToggle={handleToggle} theme={theme}/>

      <div
        style={{
          color: theme.foreground,
          background: theme.background,
          margin: `0 auto`,
          maxWidth: 960,
          padding: `10rem 1.0875rem 1.45rem`,
        }}
      >
        <main>{children}</main>
        <footer>
          © {new Date().getFullYear()}, Built with
          {` `}
          <a href="https://www.gatsbyjs.org">Gatsby</a>
        </footer>
      </div>

    </ThemeContext.Provider>

  )
}

Layout.propTypes = {
  children: PropTypes.node.isRequired,
}

export default Layout

The Header component will look like:

import { Link } from "gatsby"
import PropTypes from "prop-types"
import React, { useContext } from "react"
import {styles} from './styles'
import { ThemeContext } from "../Context/Theme";

I will use Context to compare what is the current theme and handleToggle function to change between themes.

function Header({ siteTitle, handleToggle, theme }) {
  const themes = useContext(ThemeContext);

  return (
    <header
      style={styles(theme).header}
    >
      <div
        style={styles(theme).navbar}
      >
        <h1 style={styles(theme).title}>
          <Link
            to="/"
            style={styles(theme).link}
          >
            {siteTitle}
          </Link>
        </h1>
        <div style={styles(theme).buttonContainer}>

          <button type="button" onClick={handleToggle} style={styles(theme).toggle}>
            { theme === themes.light ? '☽' : '☼' }
          </button>

        </div>
      </div>
    </header>
  );
}

Header.propTypes = {
  siteTitle: PropTypes.string,
}

Header.defaultProps = {
  siteTitle: ``,
}

export default Header

Wrapping up

The main idea is to know that you can apply this to any site ;)

Comments

[Kira]

Hi, I used the same way to build my theme, however, the children component inside couldn't get ThemeContext... Do you know how to solve it?

[Jose Miguel]

Also look that I only themed the Header component, Main and Footer components need the prop theme or reach themes via useContext

[Jose Miguel]

Hi! Could you please show me a snippet of code?
Maybe you have to assign some css classes to the children

[Kira]

Hi, I found the solution. Before, I wrapped ThemeContext inside layout

export const Layout = (props)=>{
    <ThemeContext.Provider value={themes}>
    <Header/>
        {props.children}
    <Footer/>
    </ThemeContext.Provider>
}

Then in my page Blog, I coudln't get themeContext

export const Page = ()=>{
    const themes = useContext(ThemeContext) //can't get the value
    ...

    return (
        <Layout>
            page
        </Layout>
    )
}

The solution is to create a wrapRootElement in gatsby-browser.js. Then all pages could get ThemeContext's value.

const wrapRootElement =({element})=>{
    return(
    <ThemeContext.Provider value={themes}>
        {element}    
    </ThemeContext.Provider>
    )
}