Anki has a night mode. It even supports custom CSS rules using the class .night_mode. But there is a better way to do it:
The prefers-color-scheme media query is used to detect if the user has requested a light or dark color theme.
So I request the following feature:
When night mode is enabled prefers-color-scheme: dark should be triggered.
For a demonstration check this out:
In the options section you will see three options: Dark and Light but also an automatic mode which makes use of prefers-color-scheme. When is the system is in dark mode, the css will also load a dark color scheme.