Auto Dark Mode for Quarto

Bring automatic dark mode to Quarto web documents (webpages, slides, articles, etc.).

Installing

quarto add gadenbuie/quarto-auto-dark

This will install the extension under the _extensions subdirectory. If you’re using version control, you will want to check in this directory.

Using

To use the extension, include auto-dark in the list of filters in your document metadata or in your _quarto.yml configuration file.

filters:
  - auto-dark

When a user visits your webpage or slides at night — or whenever their operating system is set to use dark mode — an automatic dark mode is applied.

For best results in Quarto webpages, choose a single light-based theme for your page or site, and do not use Quarto’s dark mode feature.

# Do this
theme:
  light: flatly

# Don't do this
theme:
  light: flatly
  dark: darkly

Example

This page is an example! Try changing your system settings to dark mode, or just come back to this page tomorrow or later tonight, to see auto dark mode in action.

About

Quarto auto dark mode builds on a CSS-only approach to dark mode outlined by Aral Balkan in his post Implementing dark mode in a handful of lines of CSS with CSS filters.

Auto dark mode does not provide a light/dark switch and we recommend you do not include one. Instead follow the user’s operating system. All phones, tablets and modern operating systems provide conveniences to choose between light and dark user interfaces.

Our view is that a light/dark switch is only necessary if your users need to choose a color scheme that differs from the state of their operating system, which is increasingly unlikely for most websites.

At its core, auto dark mode is built on two key ideas:

First, it uses a prefers-color-scheme: dark CSS media query to set styles when the operating system is in dark mode. You can use this approach in your own CSS styles:

/* Make bold things red by default */
strong {
  color: "red"
}

@media (prefers-color-scheme: dark) {
 /* In dark mode, use blue for bold text */
 strong {
   color: "blue"
 }
}

@media (prefers-color-scheme: light) {
  /* You can also be specific about light mode */
  strong {
   color: "green"
  }
}

In dark mode, auto dark mode inverts all of the colors on the page, while trying to keep hue consistent.
```
@media (prefers-color-scheme: dark) {
  /* Invert all elements on the body while attempting to not alter the hue substantially. */
  body {
    filter: invert(100%) hue-rotate(180deg);
  }
}
```
This is definitely a big hammer approach to dark mode, but in most cases it works well and you can read more about it in Aral’s blog post.

If you want a particular element to retain its original colors, apply the same filter rule to repeat the inversion. Auto dark mode does this for images, SVGs and icons by default.
```
@media (prefers-color-scheme: dark) {
  /* Do not invert media (revert the invert). */
  img, video, iframe, svg:not(.bi, .fa) {
    filter: invert(100%) hue-rotate(180deg);
  }
}
```