Fix themes colors by using SCSS variables

[madmath03]

Description

Fix hardcoded colors preventing correct theming.

Funded by @Monogramm.

Related issues

This PR will fix themes displays, like listed in https://framagit.org/framasoft/peertube/official-plugins/-/issues/21 of peertube-theme-dark.

Has this been tested?

• 👍 yes, I added tests to the test suite
• 👍 yes, light tests as follows are enough
• 💭 no, because this PR is a draft and still needs work
• 🙅 no, because they aren't needed
• 🙋 no, because I need help

Screenshots

WIth dark theme:

• 

With default theme:
*

*

[Chocobozzz]

Hello,

This PR breaks the menu with the default theme

Try --menuForegroundColor and --menuBackgroundColor instead

[madmath03]

Hello,

This PR breaks the menu with the default theme

Try --menuForegroundColor and --menuBackgroundColor instead

Hi @Chocobozzz

done, it should be better now.

[Chocobozzz]

Thanks @madmath03