How to easily add dark mode to a React app

One of the most common UX requirements for an app is to add a way to toggle a dark mode for the user. Using React and just plain ol’ CSS this is easily achieved! This article assumes you have a basic understanding of React hooks.

Typically you would want to set the dark mode colors throughout the entire app to affect various different colors. In standard CSS there exist CSS variables. We can use these to change the colors of our entire app!

Code-along

First and foremost lets set the structure of our app:

 <div className="App">
    <header className="header">
        <h1>This is my navbar</h1>
    </header>
    <main className="main">Main content</main>
  </div>

Nothing out of the ordinary just a header and our content. Now, let's add a way to toggle the dark mode setting. I’ll quickly add Material-UI to prettify our app:

<div className="App">
  <header className="header">
        <h1>This is my navbar</h1>
  <Switch />
  </header>
  <main className="main">Main content</main>
</div>

Perfect! now we need to handle the state of the dark mode

const [darkMode, setDarkMode] = React.useState(false);

  const handleChange = () => {
    setDarkMode((prevState) => !prevState);
  };


  return (
    <div className="App">
      <header className="header">
        <h1>This is my navbar</h1>
        <Switch checked={darkMode} onChange={handleChange} />
      </header>
      <main className="main">Main content</main>
    </div>
  );

To explain, our dark mode is a basic toggle state that we switch with the Switch!

Next, with the basic logic out of the way, we can tackle the styling of the dark mode. To our App, header, and main classes we’ll add our CSS variables and a:

transition: all 500ms;

This to make the transition fluid for the user.

.App {
  // ..other styles
  transition: all 500ms;
  background-color: var(--bg);
}

.header {
  // ...other styles
  transition: all 500ms;
  background-color: var(--navbar);
  color: var(--color);
}

.main {
  // ...other styles
  background-color: var(--secondarybg);
  color: var(--color);
}

Great! Now all that’s left is to hook up our CSS variables with the dark mode state. React offers us a useEffect hook to do secondary effects.

 React.useEffect(() => {
    if (darkMode) {
      document.documentElement.style.setProperty("--color", "#FFFFFF");
      document.documentElement.style.setProperty("--navbar", "#333333");
      document.documentElement.style.setProperty("--bg", "#212121");
      document.documentElement.style.setProperty("--secondarybg", "#212121");
    } else {
      document.documentElement.style.setProperty("--color", "#616161");
      document.documentElement.style.setProperty("--navbar", "#FFFFFF");
      document.documentElement.style.setProperty("--bg", "#FFFFFF");
      document.documentElement.style.setProperty("--secondarybg", "#F5F5F5");
    }
  }, [darkMode]);

Dark Mode Final Implementation

And that’s everything! Let’s check it out in a working example:

Do you have a preferred way to add dark mode to your app? Let me know in the comments below.

More content at Relatable Code