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+[#]: subject: "A simple CSS trick for dark mode"
+[#]: via: "https://opensource.com/article/21/10/dark-themes-websites"
+[#]: author: "Ayush Sharma https://opensource.com/users/ayushsharma"
+[#]: collector: "lujun9972"
+[#]: translator: " "
+[#]: reviewer: " "
+[#]: publisher: " "
+[#]: url: " "
+
+A simple CSS trick for dark mode
+======
+The ability to let your website adjust to the user's theme of choice is
+a great accessibility feature.
+![Text editor on a browser, in blue][1]
+
+You're likely already familiar with media queries. They're in widespread use for making websites responsive. The `width` and `height` properties contain the viewport's dimensions. You then use CSS to render different layouts at different dimensions.
+
+The [prefers-color-scheme media query][2] works the same way. The user can configure their operating system to use a light or dark theme. `Prefers-color-scheme` contains that value. The value is either `light` or `dark`, though the W3C spec states that it might support future values like `sepia`. I specify different values of CSS variables for both modes and let the user's OS decide.
+
+### The prefers-color-scheme media queries
+
+The two variations of the `prefers-color-scheme` media query are:
+
+
+```
+/* Light mode */
+@media (prefers-color-scheme: light) {
+   :root {
+       --body-bg: #FFFFFF;
+       --body-color: #000000;
+   }
+}
+
+/* Dark mode */
+@media (prefers-color-scheme: dark) {
+   :root {
+       --body-bg: #000000;
+       --body-color: #FFFFFF;
+   }
+}
+```
+
+In the above CSS, `--body-bg` and `--body-color` are [CSS variables][3]. As you can see, they contain different values for both modes. In the light theme, I'm setting a white background with black text. In the dark theme, I'm setting black background with white text.
+
+Since the [spec][2] says that W3C might introduce future values, it makes sense to convert this CSS into a boolean.
+
+
+```
+/* Light mode */
+:root {
+   --body-bg: #FFFFFF;
+   --body-color: #000000;
+}
+
+/* Dark mode */
+@media (prefers-color-scheme: dark) {
+   :root {
+       --body-bg: #000000;
+       --body-color: #FFFFFF;
+   }
+}
+```
+
+In the above code, I'm defining a light theme by default and converting it to the dark theme if the media query is `dark`. This way, any future values added to the media query will set the light theme by default.
+
+### Using the CSS variables
+
+Now that I have different values for different themes, I need to actually use them to style the page.
+
+
+```
+body {
+   background: var(--body-bg);
+   color: var(--body-color);
+}
+```
+
+The [var() syntax][3] is how CSS uses variables. In the above code, I'm saying set the `background` to the value of `--body-bg` and set the `color` to the value of `--body-color`. Note that the values of these variables are coming from the media query. Meaning that the background and foreground color changes based on the OS's setting! 
+
+This is the real power of the media query: Providing a consistent user experience from OS to the web page.
+
+If you go to [findmymastodon.com][4] and switch your OS's theme, you'll see the transition from one theme to the other.
+
+The [CSS Working Group][2] website also uses the same media queries. Change your OS theme, and the website switches themes to adjust.
+
+### Conclusion
+
+Notice that using `prefers-color-scheme` is no different from using a regular programming language. I define variables whose values change based on some logic. And those variables are then used for further operations.
+
+The ability to let your website adjust to the user's theme of choice is a great accessibility feature. And it further blurs the line between desktop and web for the benefit of the user. The latest browser versions [support prefers-color-scheme][5], so you can begin experimenting today.
+
+Happy coding.
+
+* * *
+
+_This article originally appeared on the [author's website][6] and is republished with permission._
+
+--------------------------------------------------------------------------------
+
+via: https://opensource.com/article/21/10/dark-themes-websites
+
+作者：[Ayush Sharma][a]
+选题：[lujun9972][b]
+译者：[译者ID](https://github.com/译者ID)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
+
+[a]: https://opensource.com/users/ayushsharma
+[b]: https://github.com/lujun9972
+[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/browser_blue_text_editor_web.png?itok=lcf-m6N7 (Text editor on a browser, in blue)
+[2]: https://drafts.csswg.org/mediaqueries-5/#prefers-color-scheme
+[3]: https://www.w3.org/TR/css-variables-1/
+[4]: https://findmymastodon.com/
+[5]: https://caniuse.com/prefers-color-scheme
+[6]: https://ayushsharma.in/2021/10/creating-light-and-dark-themes-for-websites-correctly-using-prefers-color-scheme