`prefers-color-scheme` is incorrect when using light default in Night theme

[romilbhardwaj]

GitHub seems to set the prefers-color-scheme CSS property to dark when using the light default in Night theme. Using the example from github docs:

<picture>
  <source media="(prefers-color-scheme: dark)" srcset="https://user-images.githubusercontent.com/25423296/163456776-7f95b81a-f1ed-45f7-b7ab-8fa810d529fa.png">
  <source media="(prefers-color-scheme: light)" srcset="https://user-images.githubusercontent.com/25423296/163456779-a8556205-d0a5-45e2-ac17-42d089e3c3f8.png">
  <img alt="Shows an illustrated sun in light color mode and a moon with stars in dark color mode." src="https://user-images.githubusercontent.com/25423296/163456779-a8556205-d0a5-45e2-ac17-42d089e3c3f8.png">
</picture>

This renders as:

The expected output should have been:

Replication

This happens only when you use the following settings:

1. System OS is in dark mode
2. In github settings -> appearance: Theme mode: Sync with system
3. Light default is selected for the Night theme

Here is the configuration:

When this configuration is used, the github page sets prefers-color-scheme: dark even though the page is rendered in light mode.

[janosh]

Same problem here, just the other way round: seeing a dark image where a light one was expected due to using "Theme mode: Sync with system" and light mode is set to "Dark Dimmed".

Expected	Actual

[Thyodas]

The feature is still not working today with Sync with system

[github-actions[bot]]

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