Introduce dark mode about oioioi HOT 2 OPEN

I am still not convinced we are ready for such a feature:

• Current UI needs to be available in (at least) 2 color schemes. I have not seen yet any suggestions.
• Not all materials are available in the source code. Some problems might become unreadable after changes and we have 1000s of them. Testing them seems to be very time consuming process.
• There are rules regarding presenting logos, which must be followed (some research needed)
• All future changes in UI would require more work like designing many color schemes or modifying already-formated data. I find our team too small for this extra work.

** Example workaround: **

Recommend an open source extension which inverts colors of all entities on a website. Contrast will be fine, but colors will be off. This solution feels easier and more robust.

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@MasloMaslane said:

I’m using [this](https://github.com/darkreader/darkreader) extension for dark theme and it works quite well on SIO

I think that we could inform our users about the possibility of using such an extension. I would say it is a good compromise between helping users and making our UI more complex to maintain. Feel free to recommend other tools, which work well or/and proper notification text at least in English or/and even a pull request!

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