Overhyped or necessity? Learn everything about dark mode and how to support it to the benefit of your users!
 Thomas Steiner [GitHub](https://github.com/tomayac) [LinkedIn](https://www.linkedin.com/in/thomassteinerlinkedin) [Mastodon](https://toot.cafe/@tomayac) [Bluesky](https://bsky.app/profile/tomayac.com) [Homepage](https://blog.tomayac.com/)
## Introduction
> [!NOTE]
> **Note:** I have done a lot of background research on the history and theory of dark mode, if you are only interested in working with dark mode, feel free to [skip the introduction](https://web.dev/articles/prefers-color-scheme.md.txt#activating_dark_mode_in_the_operating_system).
### Dark mode before *Dark Mode*
 Green screen ([Source](https://commons.wikimedia.org/wiki/File:Compaq_Portable_and_Wordperfect.JPG))
We have gone full circle with dark mode.
In the dawn of personal computing, dark mode wasn't a matter of choice,
but a matter of fact:
Monochrome computer monitors worked by firing electron beams
on a phosphorescent screen and the phosphor used in early CRTs was green.
Because text was displayed in green and the rest of the screen was black, these models were often referred to as
[green screens](https://commons.wikimedia.org/wiki/File:Schneider_CPC6128_with_green_monitor_GT65,_start_screen.jpg).
 Dark-on-white ([Source](https://www.youtube.com/watch?v=qKkABzt0Zqg))
The subsequently introduced Color CRTs displayed multiple colors
through the use of red, green, and blue phosphors.
They created white by activating all three phosphors simultaneously.
With the advent of more sophisticated
[desktop publishing](https://en.wikipedia.org/wiki/Desktop_publishing),
the idea of making the virtual document resemble a physical sheet of paper became popular.
 The WorldWideWeb browser ([Source](https://commons.wikimedia.org/wiki/File:WorldWideWeb_FSF_GNU.png))
This is where *dark-on-white* as a design trend started,
and this trend was carried over to the
[early document-based web](http://info.cern.ch/hypertext/WWW/TheProject.html).
The first ever browser,
[WorldWideWeb](https://en.wikipedia.org/wiki/WorldWideWeb)
(remember,
[CSS wasn't even invented](https://en.wikipedia.org/wiki/Cascading_Style_Sheets#History) yet),
displayed webpages this way.
Fun fact: the second-ever browser,
[Line Mode Browser](https://en.wikipedia.org/wiki/Line_Mode_Browser)---a terminal-based browser---was
green on dark.
These days, web pages and web apps are typically designed with dark text
on a light background, a baseline assumption that is also hard-coded in user agent stylesheets, including
[Chrome's](https://chromium.googlesource.com/chromium/blink/+/master/Source/core/css/html.css).
 Mobile phone used in bed
The days of CRTs are long over.
Content consumption and creation has shifted to mobile devices
that use backlit
or energy-saving screens.
Smaller and more transportable computers, tablets, and smartphones led to new usage patterns.
Leisure tasks like web browsing, coding for fun, and high-end gaming
frequently happen after-hours in dim environments.
People even enjoy their devices in their beds at night-time.
The more people use their devices in the dark,
the more the idea of going back to the roots of *light-on-dark* becomes popular.
### Why dark mode
#### Dark mode for aesthetic reasons
When people get asked
[why they like or want dark mode](https://medium.com/dev-channel/let-there-be-darkness-maybe-9facd9c3023d),
the most popular response is that *"it's easier on the eyes,"*
followed by *"it's elegant and beautiful."*
Apple in their
[Dark Mode developer documentation](https://developer.apple.com/documentation/appkit/supporting_dark_mode_in_your_interface)
explicitly writes: *"The choice of whether to enable a light or dark appearance
is an aesthetic one for most users, and might not relate to ambient lighting conditions."*
> [!NOTE]
> **Note:** Read up more on [user research regarding why people want dark mode and how they use it](https://medium.com/dev-channel/let-there-be-darkness-maybe-9facd9c3023d).
 CloseView in Mac OS System 7 with "White on Black" mode ([Source](https://archive.org/details/mac_Macintosh_System_7_at_your_Fingertips_1992))
#### Dark mode as an accessibility tool
There are also people who actually *need* dark mode and use it as another accessibility tool,
for example, users with low vision.
The earliest occurrence of such an accessibility tool I could find is
[System 7](https://en.wikipedia.org/wiki/System_7)'s *CloseView* feature, which had a toggle for
*Black on White* and *White on Black*.
While System 7 supported color, the default user interface was still black-and-white.
These inversion-based implementations demonstrated their weaknesses once color was introduced.
User research by Szpiro *et al.* on
[how people with low vision access computing devices](https://dl.acm.org/citation.cfm?id=2982168)
showed that all interviewed users disliked inverted images,
but that many preferred light text on a dark background.
Apple accommodates for this user preference with a feature called
[Smart Invert](https://www.apple.com//accessibility/iphone/vision/),
which reverses the colors on the display, except for images, media,
and some apps that use dark color styles.
A special form of low vision is Computer Vision Syndrome, also known as Digital Eye Strain, which is
[defined](https://onlinelibrary.wiley.com/doi/full/10.1111/j.1475-1313.2011.00834.x)
as *"the combination of eye and vision problems associated with the use of computers
(including desktop, laptop, and tablets) and other electronic displays (e.g.
smartphones and electronic reading devices)."*
It has been [proposed](https://bmjopen.bmj.com/content/5/1/e006748)
that the use of electronic devices by adolescents, particularly at night time,
leads to an increased risk of shorter sleep duration,
longer sleep-onset latency, and increased sleep deficiency.
Additionally, exposure to blue light has been widely
[reported](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4254760/)
to be involved in the regulation of
[circadian rhythm](https://en.wikipedia.org/wiki/Circadian_rhythm)
and the sleep cycle,
and irregular light environments may lead to sleep deprivation,
possibly affecting mood and task performance, according to
[research by Rosenfield](https://www.college-optometrists.org/oip-resource/computer-vision-syndrome--a-k-a--digital-eye-strain.html).
To limit these negative effects, reducing blue light by adjusting the display color temperature
through features like iOS' [Night Shift](https://support.apple.com/en-us/HT207570) or Android's
[Night Light](https://support.google.com/pixelphone/answer/7169926) can help,
as well as avoiding bright lights or irregular lights in general through dark themes or dark modes.
#### Dark mode power savings on AMOLED screens
Finally, dark mode is known to save a *lot* of energy on
screens.
Android case studies that focused on popular Google apps
like YouTube have shown that the power savings can be up to 60%.
The video below has more details on these case studies and the power savings per app.
[Video](https://www.youtube.com/watch?v=N_6sPd0Jd3g)
## Activating dark mode in the operating system
Now that I have covered the background of why dark mode is such a big deal for many users,
let's review how you can support it.
 Android Q dark mode settings
Operating systems that support a dark mode or dark theme
typically have an option to activate it somewhere in the settings.
On macOS X, it's in the system preference's *General* section and called *Appearance* ([screenshot](https://web.dev/articles/prefers-color-scheme/image/light-dark-theme-settings.png?auto=format)),
and on Windows 10, it's in the *Colors* section and called *Choose your color* ([screenshot](https://web.dev/articles/prefers-color-scheme/image/choose-your-color.png?auto=format)).
For Android Q, you can find it under *Display* as a *Dark Theme* toggle switch ([screenshot](https://web.dev/articles/prefers-color-scheme/image/android-display-dark.png?auto=format)),
and on iOS 13, you can change the *Appearance* in the *Display \& Brightness*
section of the settings ([screenshot](https://web.dev/articles/prefers-color-scheme/image/android-light-dark-theme.jpg?auto=format)).
## The `prefers-color-scheme` media query
One last bit of theory before I get going.
[Media queries](https://developer.mozilla.org/docs/Web/CSS/Media_Queries/Using_media_queries)
allow authors to test and query values or features of the user agent or display device,
independent of the document being rendered.
They are used in the CSS `@media` rule to conditionally apply styles to a document,
and in various other contexts and languages, such as HTML and JavaScript.
[Media Queries Level 5](https://drafts.csswg.org/mediaqueries-5/)
introduces so-called user preference media features, that is,
a way for sites to detect the user's preferred way to display content.
> [!NOTE]
> **Note:** ☝️ An established user preference media feature is `prefers-reduced-motion` that lets you detect the desire for less motion on a page. I have [written about `prefers-reduced-motion`](https://web.dev/prefers-reduced-motion) before.
The [`prefers-color-scheme`](https://drafts.csswg.org/mediaqueries-5/#prefers-color-scheme)
media feature is used to detect
if the user has requested the page to use a light or dark color theme.
It works with the following values:
- `light`: Indicates that the user has notified the system that they prefer a page that has a light theme (dark text on light background).
- `dark`: Indicates that the user has notified the system that they prefer a page that has a dark theme (light text on dark background).
> [!NOTE]
> **Note:** An earlier version of the spec included a third value, `no-preference`. It was meant to indicate that the user has made no preference known to the system. Since no browser ever implemented it, the value was [removed](https://github.com/w3c/csswg-drafts/issues/3857#issuecomment-634779976) from the spec.
## Supporting dark mode
### Finding out if dark mode is supported by the browser
As dark mode is reported through a media query, you can easily check if the current browser
supports dark mode by checking if the media query `prefers-color-scheme` matches at all.
Note how I don't include any value, but purely check if the media query alone matches.
```javascript
if (window.matchMedia('(prefers-color-scheme)').media !== 'not all') {
console.log('🎉 Dark mode is supported');
}
```
At the time of writing, `prefers-color-scheme` is supported on both desktop and mobile (where available)
by Chrome and Edge as of version 76, Firefox as of version 67,
and Safari as of version 12.1 on macOS and as of version 13 on iOS.
For all other browsers, you can check the [Can I use support tables](https://caniuse.com/#feat=prefers-color-scheme) document.
> [!NOTE]
> **Note:** There is a custom element [``](https://github.com/GoogleChromeLabs/dark-mode-toggle) available that adds dark mode support to older browsers. I write about it [further down in this article](https://web.dev/articles/prefers-color-scheme.md.txt#the_dark-mode-toggle_custom_element).
### Learning about a user's preferences at request time
The [`Sec-CH-Prefers-Color-Scheme`](https://web.dev/articles/user-preference-media-features-headers.md.txt) client hint header
allows sites to obtain the user's color scheme preferences optionally at request time,
allowing servers to inline the right CSS and therefore avoid a flash of incorrect color theme.
### Dark mode in practice
Let's finally see how supporting dark mode looks like in practice.
Just like with the [Highlander](https://web.dev/%3Chttps://en.wikipedia.org/wiki/Highlander_(film)%3E),
with dark mode *there can be only one* : dark or light, but never both!
Why do I mention this? Because this fact should have an impact on the loading strategy.
**Please don't force users to download CSS in the critical rendering path
that is for a mode they don't currently use.**
To optimize load speed, I have therefore split my CSS for the example app
that shows the following recommendations in practice
into three parts in order to [defer non-critical CSS](https://web.dev/articles/defer-non-critical-css.md.txt):
- `style.css` that contains generic rules that are used universally on the site.
- `dark.css` that contains only the rules needed for dark mode.
- `light.css` that contains only the rules needed for light mode.
### Loading strategy
The two latter ones, `light.css` and `dark.css`,
are loaded conditionally with a `` query.
Initially,
[not all browsers will support `prefers-color-scheme`](https://caniuse.com/#feat=prefers-color-scheme)
(detectable using the [pattern above](https://web.dev/articles/prefers-color-scheme.md.txt#finding_out_if_dark_mode_is_supported_by_the_browser)),
which I deal with dynamically by loading the default `light.css` file
via a conditionally inserted `` element in a minuscule inline script
(light is an arbitrary choice, I could also have made dark the default fallback experience).
To avoid a [flash of unstyled content](https://en.wikipedia.org/wiki/Flash_of_unstyled_content),
I hide the content of the page until `light.css` has loaded.
```html
```
### Stylesheet architecture
I make maximum use of [CSS variables](https://developer.mozilla.org/docs/Web/CSS/var),
this allows my generic `style.css` to be, well, generic,
and all the light or dark mode customization happens in the two other files `dark.css` and `light.css`.
Below you can see an excerpt of the actual styles, but it should suffice to convey the overall idea.
I declare two variables, `--color` and `--background-color`
that essentially create a *dark-on-light* and a *light-on-dark* baseline theme.
```css
/* light.css: 👉 dark-on-light */
:root {
--color: rgb(5, 5, 5);
--background-color: rgb(250, 250, 250);
}
```
```css
/* dark.css: 👉 light-on-dark */
:root {
--color: rgb(250, 250, 250);
--background-color: rgb(5, 5, 5);
}
```
In my `style.css`, I then use these variables in the `body { ... }` rule.
As they are defined on the
[`:root` CSS pseudo-class](https://developer.mozilla.org/docs/Web/CSS/:root)---a
selector that in HTML represents the `` element
and is identical to the selector `html`, except that its specificity is
higher---they cascade down, which serves me for declaring global CSS variables.
```css
/* style.css */
:root {
color-scheme: light dark;
}
body {
color: var(--color);
background-color: var(--background-color);
}
```
In the code sample above, you will probably have noticed a property
[`color-scheme`](https://drafts.csswg.org/css-color-adjust-1/#propdef-color-scheme)
with the space-separated value `light dark`.
This tells the browser which color themes my app supports
and allows it to activate special variants of the user agent stylesheet,
which is useful to, for example, let the browser render form fields
with a dark background and light text, adjust the scroll bars,
or to enable a theme-aware highlight color.
The exact details of `color-scheme` are specified in
[CSS Color Adjustment Module Level 1](https://drafts.csswg.org/css-color-adjust-1/).
> [!NOTE]
> **Note:** 🌒 Read up more on [what `color-scheme` actually does](https://web.dev/articles/color-scheme.md.txt).
Everything else is then just a matter of defining CSS variables
for things that matter on my site.
Semantically organizing styles helps a lot when working with dark mode.
For example, rather than `--highlight-yellow`, consider calling the variable
`--accent-color`, as "yellow" may actually not be yellow in dark mode or vice versa.
Below is an example of some more variables that I use in my example.
```css
/* dark.css */
:root {
--color: rgb(250, 250, 250);
--background-color: rgb(5, 5, 5);
--link-color: rgb(0, 188, 212);
--main-headline-color: rgb(233, 30, 99);
--accent-background-color: rgb(0, 188, 212);
--accent-color: rgb(5, 5, 5);
}
```
```css
/* light.css */
:root {
--color: rgb(5, 5, 5);
--background-color: rgb(250, 250, 250);
--link-color: rgb(0, 0, 238);
--main-headline-color: rgb(0, 0, 192);
--accent-background-color: rgb(0, 0, 238);
--accent-color: rgb(250, 250, 250);
}
```
### Full example
In the following [embedded demo](https://googlechrome.github.io/samples/glitch-migration/darkmode/baseline/),
you can see the complete example that puts the concepts from above into practice.
Try toggling dark mode in your particular [operating system's settings](https://web.dev/articles/prefers-color-scheme.md.txt#activating_dark_mode_in_the_operating_system)
and see how the page reacts.
### Loading impact
When you play with this example, you can see
why I load my `dark.css` and `light.css` via media queries.
Try toggling dark mode and reload the page:
the particular currently non-matching stylesheets are still loaded, but with the lowest priority,
so that they never compete with resources that are needed by the site right now.
> [!NOTE]
> **Note:** 😲 Read up more on [why browsers download stylesheets with non-matching media queries](https://blog.tomayac.com/2018/11/08/why-browsers-download-stylesheets-with-non-matching-media-queries-180513).
 Site in light mode loads the dark mode CSS with lowest priority.  Site in dark mode loads the light mode CSS with lowest priority.  Site in default light mode on a browser that doesn't support `prefers-color-scheme` loads the dark mode CSS with lowest priority.
### Reacting on dark mode changes
Like any other media query change, dark mode changes can be subscribed to via JavaScript.
You can use this to, for example, dynamically change the
[favicon](https://developers.google.com/web/fundamentals/design-and-ux/browser-customization/#provide_great_icons_tiles)
of a page or change the
[``](https://developers.google.com/web/fundamentals/design-and-ux/browser-customization/#meta_theme_color_for_chrome_and_opera)
that determines the color of the URL bar in Chrome.
The [full example](https://web.dev/articles/prefers-color-scheme.md.txt#full_example) above shows this in action,
in order to see the theme color and favicon changes, open the
[demo in a separate tab](https://googlechrome.github.io/samples/glitch-migration/darkmode/baseline/).
```javascript
const darkModeMediaQuery = window.matchMedia('(prefers-color-scheme: dark)');
darkModeMediaQuery.addEventListener('change', (e) => {
const darkModeOn = e.matches;
console.log(`Dark mode is ${darkModeOn ? '🌒 on' : '☀️ off'}.`);
});
```
As of Chromium 93 and Safari 15, you can adjust the color based on a
media query with the `media` attribute of the `meta` theme color element. The
first one that matches will be picked. For example, you could have one color for
light mode and another one for dark mode. At the time of writing, you can't
define those in your manifest. See [w3c/manifest#975 GitHub
issue](https://github.com/w3c/manifest/issues/975).
```html
```
## Debugging and testing dark mode
### Emulating `prefers-color-scheme` in DevTools
Switching the entire operating system's color scheme can get annoying real quick,
so Chrome DevTools now allows you to emulate the user's preferred color scheme
in a way that only affects the currently visible tab.
Open the [Command Menu](https://developer.chrome.com/docs/devtools/command-menu), start typing `Rendering`, run the `Show Rendering` command, and then change the **Emulate CSS media feature prefers-color-scheme** option.
### Screenshotting `prefers-color-scheme` with Puppeteer
[Puppeteer](https://github.com/GoogleChrome/puppeteer/) is a Node.js library
that provides a high-level API to control Chrome or Chromium over the
[DevTools Protocol](https://chromedevtools.github.io/devtools-protocol/).
With [`dark-mode-screenshot`](https://www.npmjs.com/package/dark-mode-screenshot), we provide
a Puppeteer script that lets you create screenshots of your pages in both dark and light mode.
You can run this script as a one-off, or alternatively make it part of your
Continuous Integration (CI) test suite.
```bash
npx dark-mode-screenshot --url https://googlechromelabs.github.io/dark-mode-toggle/demo/ --output screenshot --fullPage --pause 750
```
## Dark mode best practices
### Avoid pure white
A small detail you may have noticed is that I don't use pure white.
Instead, to prevent glowing and bleeding against the surrounding dark content,
I choose a slightly darker white. Something like `rgb(250, 250, 250)` works well.
### Re-colorize and darken photographic images
If you compare the two screenshots below, you will notice that not only the core theme has changed
from *dark-on-light* to *light-on-dark* , but that also the hero image looks slightly different.
My [user research](https://medium.com/dev-channel/re-colorization-for-dark-mode-19e2e17b584b)
has shown that the majority of the surveyed people
prefer slightly less vibrant and brilliant images when dark mode is active.
I refer to this as *re-colorization*.
 Hero image slightly darkened in dark mode.  Regular hero image in light mode.
Re-colorization can be achieved through a CSS filter on my images.
I use a CSS selector that matches all images that don't have `.svg` in their URL,
the idea being that I can give vector graphics (icons) a different re-colorization treatment
than my images (photos), more about this in the [next paragraph](https://web.dev/articles/prefers-color-scheme.md.txt#invert_vector_graphics_and_icons).
Note how I again use a [CSS variable](https://developer.mozilla.org/docs/Web/CSS/var),
so I can later on flexibly change my filter.
> [!NOTE]
> **Note:** 🎨 Read up more on [user research regarding re-colorization preferences with dark mode](https://medium.com/dev-channel/re-colorization-for-dark-mode-19e2e17b584b).
As re-colorization is only needed in dark mode, that is, when `dark.css` is active,
there are no corresponding rules in `light.css`.
```css
/* dark.css */
--image-filter: grayscale(50%);
img:not([src*='.svg']) {
filter: var(--image-filter);
}
```
#### Customizing dark mode re-colorization intensities with JavaScript
Not everyone is the same and people have different dark mode needs.
By sticking to the re-colorization method described above,
I can easily make the grayscale intensity a user preference that I can
[change via JavaScript](https://developer.mozilla.org/docs/Web/CSS/Using_CSS_custom_properties#Values_in_JavaScript),
and by setting a value of `0%`, I can also disable re-colorization completely.
Note that [`document.documentElement`](https://developer.mozilla.org/docs/Web/API/Document/documentElement)
provides a reference to the root element of the document,
that is, the same element I can reference with the
[`:root` CSS pseudo-class](https://developer.mozilla.org/docs/Web/CSS/:root).
```javascript
const filter = 'grayscale(70%)';
document.documentElement.style.setProperty('--image-filter', value);
```
### Invert vector graphics and icons
For vector graphics---that in my case are used as icons that I reference via `` elements---I
use a different re-colorization method.
While [research](https://dl.acm.org/citation.cfm?id=2982168) has shown
that people don't like inversion for photos, it does work very well for most icons.
Again I use CSS variables to determine the inversion amount
in the regular and in the [`:hover`](https://developer.mozilla.org/docs/Web/CSS/:hover) state.
 Icons are inverted in dark mode.  Regular icons in light mode.
Note how again I only invert icons in `dark.css` but not in `light.css`, and how `:hover`
gets a different inversion intensity in the two cases to make the icon appear
slightly darker or slightly brighter, dependent on the mode the user has selected.
```css
/* dark.css */
--icon-filter: invert(100%);
--icon-filter_hover: invert(40%);
img[src*='.svg'] {
filter: var(--icon-filter);
}
```
```css
/* light.css */
--icon-filter_hover: invert(60%);
```
```css
/* style.css */
img[src*='.svg']:hover {
filter: var(--icon-filter_hover);
}
```
### Use `currentColor` for inline SVGs
For *inline* SVG images, instead of [using inversion filters](https://web.dev/articles/prefers-color-scheme.md.txt#invert_vector_graphics_and_icons),
you can leverage the [`currentColor`](https://developer.mozilla.org/docs/Web/CSS/color_value#currentColor_keyword)
CSS keyword that represents the value of an element's `color` property.
This lets you use the `color` value on properties that do not receive it by default.
Conveniently, if `currentColor` is used as the value of the SVG
[`fill` or `stroke` attributes](https://developer.mozilla.org/docs/Web/SVG/Tutorial/Fills_and_Strokes#Fill_and_Stroke_Attributes),
it instead takes its value from the inherited value of the color property.
Even better: this also works for
[``](https://developer.mozilla.org/docs/Web/SVG/Element/use),
so you can have separate resources
and `currentColor` will still be applied in context.
Please note that this only works for *inline* or `