Themes 🎨 🤩

Not everyone likes to read on vanilla setup with white background and black text color. Therefore we'll add few awesome themes to choose from.

We'll setup two themes and some kind of control to switch between them.

Following are the steps we'll do for this:

  • Define theme (no code. just thinking)
  • Tell tailwind about the definition
  • Create instances of the theme definition
  • Refactor code to utilise these new themes
  • Implement a control to switch themes
  • Persist user selection

Theme definition

Theme is nothing but a set of colors that we apply to different parts of our website.

So the first thing we need to do is to decide following:

  • a) What are the parts of the website for which we want to change color on theme switching?
  • b) What all colors do we need for those parts? (we'll talk about this while creating theme instances)

For this blog, I could think of following parts as of now:

  • background color for the html
  • background color for the content block
  • background color the code section
  • text color


Inform tailwind

Now that we have decided on the parts we want to color. Next step is tell tailwind about these variables.

For this we'll edit tailwind.config.js and extend the theme object by adding keys for these colors to it as follows:

module.exports = {
  corePlugins: {
    // preflight: false,
  purge: ["./src/**/*.js", "./src/**/*.jsx", "./src/**/*.ts", "./src/**/*.tsx"],
  theme: {
    extend: {
      textColor: {
        default: "var(--color-text-default)",
      backgroundColor: {
        html: "var(--color-bg-html)",
        content: "var(--color-bg-content)",
        block: "var(--color-bg-block)",
  variants: {},
  plugins: [],

Theme instances

This is the fun part 🤩, where I get to play with colors to define different themes for our blog.

I am going to define two themes for now (may be more later bcz its fun):

  • Vanilla (plain, default, basic white-gray based theme)
  • Tang

And we'll assign color to each decided part per theme.

For this I've added following to a new file src/css/themes.css:

.theme-vanilla {
  --color-bg-html: theme("colors.white");
  --color-bg-content: theme("colors.gray.100");
  --color-bg-block: theme("colors.gray.200");
  --color-text-default: theme("colors.gray.900");

.theme-tang {
  --color-bg-html: #fffcf9;
  --color-bg-content: #fff4e8;
  --color-bg-block: #ffddbb;
  --color-text-default: #553344;

Notice how i am assigning color hex values in two different ways.

  1. In vanilla, I have used colors from tailwind
  2. In sunset, I have hardcoded the specific values

and imported it in src/css/index.css as follows:

@import "themes.css";

Using themes

We are all set to use the themes now. We just need to target the right html element and assign it the right className.

So basically, we need to assign className for:

  • 4 background colors (bg-html, bg-content, bg-block, text-default)
  • 1 theme name (theme-vanilla or theme-tang)

bg colors

Following is how I've assigned the bg colors:

  • bg-html & text-default is assigned to the root div of Layout.js
  • bg-content is assigned to main element of Content.js
  • bg-block is assigned to code css block in src/css/unreset.css

theme name

  • theme class is assigned to the root div of Layout.js

Persist the theme !

  • useState hook is used to store theme value in Layout.js with initial value set to vanilla.
  • localStorage is used to persist the user selected theme value.
  • window object is being checked, because web APIs are not available while SSR (server side rendering)
  • useEffect hook is used to write to localStorage and set the themeName to render the correct theme on first load.

So below is content of Layout.js:

function Layout({ children, title }) {
  const [theme, setTheme] = useState(() => {
    if (typeof window !== `undefined`) {
      let themeLS = localStorage.getItem("theme")
        ? localStorage.getItem("theme")
        : "vanilla";
      return themeLS;
    } else {
      return "vanilla";
  const [themeName, setThemeName] = useState("theme-vanilla");

  useEffect(() => {
    window.localStorage.setItem("theme", theme);
  }, [theme]);

  return (
    <div className={`${themeName} bg-html text-default`}>
      <Helmet title={title} />
      <div className="w-full max-w-4xl mx-auto flex flex-col min-h-screen font-sans">
        <Header theme={theme} setTheme={setTheme} />
        <main className="flex-1 px-2 py-2">{children}</main>

Switch control

I am passing both theme and setTheme to Header.js, where I have implemented the controls to switch the theme:

import React, { useState, useEffect } from "react";
import { Link } from "gatsby";

function Header({ theme, setTheme }) {
  const [isMenuOpen, setMenuOpen] = useState(false);

  return (
    <nav className="">
      <div className="flex items-center justify-between px-2 py-3 ">
        <div className="">
            <Link className="no-underline" to="/">
        <div className="">
            className="block text-gray-600 focus:outline-none"
            onClick={() => setMenuOpen(!isMenuOpen)}
              className="h-6 w-6"
              viewBox="0 0 24 24"
              {isMenuOpen && (
                  // cross
                  d="M6 18L18 6M6 6l12 12"
              {!isMenuOpen && (
                  d="M12 6V4m0 2a2 2 0 100 4m0-4a2 2 0 110 4m-6 8a2 2 0 100-4m0 4a2 2 0 110-4m0 4v2m0-6V4m6 6v10m6-2a2 2 0 100-4m0 4a2 2 0 110-4m0 4v2m0-6V4"
          !isMenuOpen ? "hidden" : ""
        } flex justify-between flex-row-reverse items-center sm:items-end bg-content rounded px-8 py-4`}
        <div className="flex flex-col">
          <span className="text-xl font-medium pb-2 text-right">Themes</span>
          {["vanilla", "tang", "cappuccino"].map((themeName, index) => {
            return (
                onClick={() => setTheme(themeName)}
                  theme === themeName ? "bg-block" : ""
                } focus:outline-none text-right px-1`}
                {themeName.charAt(0).toUpperCase() + themeName.slice(1)}

export default Header;


I am aware of flash of unstyled content (FOUC). But thats may be for some other time to fix!

Thats all folks!


Following are the GitHub commits which represents what we've done in this post 🤩

  • commit 1 - Implements theming with tailwind
  • commit 2 - Fixes localStorage ain't available while ssr
  • commit 3 - Fixes correct theme not rendering on initial load
  • commit 4 - generate theme button in loop and redefine theme colors
  • commit 5 - adds new theme blackcurrant and some more theme color vars


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