Dark mode toggle button has become a norm in web development now. But we can automatically enable dark mode based on system settings using pure CSS. (No more toggle buttons)

It's as easy as adding a media query to your CSS. This is how I added automatic dark mode in my app Hoy (hoy.sh). I use variables in my app so it became much more easy to enable it.

My CSS before adding dark mode:

:root {
  --background-color: #f7f6ee;
  --secondary-color: #fbfefb;
  --text-dark: #101010;
  --text: #333333;
  --text-light: #7b7b85;
  --text-lighter: #ababab;
  --blue: #3498db;
  --green: #27ae60;
  --yellow: #feca57;
  --red: #c0392b;
  --white: #ffffff;
}
/* Sample css for an element */
body {
  background: var(--background-color);
  color: var(--text);
}

Media queries allow us to add CSS based on the system's colour preference using prefers-color-scheme. For detailed documentation refer https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-color-scheme.

So in order to enable dark mode based on the system settings, all I had to do is to add the below code in my CSS.

@media (prefers-color-scheme: dark) {
  :root {
    --background-color: #1e1f23;
    --secondary-color: #232428;
    --text-dark: #efefef;
    --text: #c4c5c9;
    --text-light: #6c6d71;
    --text-lighter: #8e8f93;
  }
}

Check out the automatic dark mode in my app at https://hoy.sh