Designs for Dark mode project (#3592)

Description

Given that users need to set the site theme from any part of the site, the most affordable area is the site footer. It already has the language selector, that behaves equally, and adding the action there is the more logical solution.

Mockups

For the current arrangement of pages in both footer content and internal, the following version is the one that convince me most.

The switcher is placed next to the language selector and it behaves equally. The options displayed are Light, Dark, and System in the OS/browser popover.

Footer

Content footer is on top and internal footer at the bottom.

Middle- and long-term idea

With the design explored (#3564) to make the internal pages area more simple, I would like to bring again the opportunity we have to make the footer even more simple by putting the general/site settings in a unique config menu.

The benefits of this idea is twofold:

• It puts Openverse in a better position with regards to privacy by making the toggle more visible
• It's the first step towards placing settings in a single menu once user profile-related actions are needed in future features.

I personally would like to consider the implementation of this middle/long-term component. What do you think?