Enable dark mode

[frmadem]

Motivation

It would be nice if we can enable the dark mode in our documentation.

We could use this.

Acceptance criteria

• [ ] Dark mode is enabled and can be activated/deactivated.
• [ ] Team acceptance.

[frmadem]

@juanjosevazquezgil you should first create a local container and test the plugin you want to use.

cc/ @gustavoborragan