[Feature Request]: Add Everforest themes and variants

[isaac-8601]

Guidelines

• [X] I have searched the issue tracker for open and closed issues that are similar to the feature request I want to file, without success.
• [X] I have searched the documentation for information that matches the description of the feature request I want to file, without success.
• [X] This issue contains only one feature request.

Problem Description

I'd like to add the Everforest theme to FreeTube's themes.

Proposed Solution

My proposed solution would be to add the Everforest variants to Freetube's theme file. There are six Everforest variants in all; three contrast variants (soft, medium/default, hard) on one axis and two mode variants (light mode, dark mode) on another axis.

I intend to add all variants to the theme list but I can just add the two medium variants if there is pushback. (I note here that some other color schemes have a lot of variants in the theme list, though!)

I am also volunteering to take on the work and submit the pull request when completed.

Alternatives Considered

There are a lot of color themes out there and a lot of generous contributors who may want to add plenty of them to FreeTube. At some point we may want to consider another way to add themes in the UI, or a custom theme CSS option accessible for users.

Issue Labels

new feature, new optional setting, visual improvement

Additional Information

No response

[bungadrum]

I already requested the Otis theme it's similar to the Everforest one

[isaac-8601]

Everforest feels more in line with similar color themes with roots in terminal emulator customization (Dracula, Catpuccin, even Nordic since it's based on Nord). At some point, it feels like this project is going to have to define theming limits and goals, or, provide some more flexible theming options for all of us our several favorite themes :smile: (I'd be up for helping strategize and design the UI for the latter.)