Offer multiple variants of "dark mode" theme

[Miyayes]

Description

As of v1.19, the dark mode in Brave was changed to a colder temperature that had better contrast properties. However, many users preferred the warmer tone of the previous dark mode. (Bluishness can also be more aggressive at night time.)

Proposed solution

Offer multiple temperatures of dark mode (e.g., a warmer one, a colder one, etc.), as proposed by @bradleyrichter. @brave/design

Community feedback

• https://www.reddit.com/r/brave_browser/comments/l1876f/design_change_earlier_the_titlebar_and_tabs_were/
• https://www.reddit.com/r/brave_browser/comments/l0utag/today_in_the_morning_i_opened_brave_and_it_was_a/
• https://www.reddit.com/r/brave_browser/comments/l168w4/browser_colors_changed/
• https://reddit.com/r/IAmA/comments/l2tvx1/we_are_brian_bondy_cofounder_and_cto_of_the_brave/gk8c54t/

[antonok-edm]

Related: https://github.com/brave/brave-browser/issues/13737

[Miyayes]

+1 https://www.reddit.com/r/brave_browser/comments/l4mqaw/is_it_possible_to_get_rid_of_the_purple_color/

[nicozagi]

+1 https://www.reddit.com/r/brave_browser/comments/l4mqaw/is_it_possible_to_get_rid_of_the_purple_color/

This question referred to the color of the private browser tabs that are always dark. Still, I would like to see color options for private and TOR browsing too!

[IAmJSD]

+1 it makes the browser extremely difficult to read for me, will probably compile a copy for myself with the old colors for my own use, but would be nice to see this in the browser

[dogekamil]

Please bring back real gray/black as default.

[joecss]

Can someone help me out with where in the code the active tab color is set for private browsing? I'd like to change it to a stronger contrast and compile locally. The recommended contrast ratio for graphic UI elements is at least 3 to 1 ( https://webaim.org/resources/contrastchecker/). For the black and purple of the private tabs, it’s only 1.3 to 1.