Add a global toggle to switch between light and dark themes

[maximousblk]

many people (read "I") prefer to use "dark mode" only at night but there is no quick way to easily toggle it if working on something. There are currently 2 ways (that I know) to toggle the dark mode: 1. settings, 2. toggle on the profile page.

It would be more convenient to move the toggle from the profile page to either the navbar or the profile dropdown on the navbar.

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alternative suggestions:

It would be even more convenient to not need to switch to dark mode manually and it would automatically switch depending on the time of the day but as mentioned in #2960, this would most probably be disabled by default and many people would want to configure at what time should the theme switch, so doesn't really fit this project but up for grabs for userscripts and the likes.

[yakov116]

Duplicate of #3802

[fregante]

it would automatically switch depending on the time of the day

I'd suggest looking into a global solution for this. macOS does so natively, for example.

[kidonng]

GitHub (sort of) implemented this, see #3802 (comment)