Add color-scheme CSS property

[renbaoshuo]

PR Checklist

• The commit message follows guidelines for NexT.
• Tests for the changes was maked (for bug fixes / features).
  • Muse | Mist have been tested.
  • Pisces | Gemini have been tested.
• Docs in NexT website have been added / updated (for features).

PR Type

• Bugfix.
• Feature.
• Code style update (formatting, local variables).
• Refactoring (no functional changes, no api changes).
• Documentation.
• Translation.
• Other... Please describe:

What is the current behavior?

What is the new behavior?

The operating system makes adjustments to the user interface when set a color-scheme value. For example, the scroll bar is adapted to the dark mode when ser color-scheme to dark.

References

https://developer.mozilla.org/en-US/docs/Web/CSS/color-scheme

[CLAassistant]

All committers have signed the CLA.

[coveralls]

Pull Request Test Coverage Report for Build 1333106300

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.468%

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Totals
Change from base Build 1320627970:	0.0%
Covered Lines:	138
Relevant Lines:	141

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💛 - Coveralls

[stevenjoezhang]

Thanks for your contribution! In February, we discussed about the solution provided in your blog in the telegram group chat of NexT. This issue is considered to be a design problem of the scroll bar on Windows (which does not exist on macOS).

[ljcbaby]

这样应该没问题了

[welcome]

Congrats on merging your first pull request here! 🎉 How awesome!

[stevenjoezhang]

@renbaoshuo Hello, the color-scheme property will not only affect the iframe, but also change the text color of the input box. Please help to fix this issue, thanks.