what is dual mode for in addition to dark/light modes

[copdips]

What's happening?

Hello,

In the dark/light mode switch, it has a third choice like:

After searching in the issues, it seems that this is called dual mode.

Anyone could give a brief description, what is it for? Because it seems that it has the same effet when I choose dark mode or dual mode.

Reproducer

switch between dark mode and dual mode

Expectation

1. more explanations the doc
2. options to disable the dual mode, sometime, dark/light is enough.

Code of Conduct

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