Dark/light theme and adaptiveness

[aramirezreyes]

Another issue following from slack.

Some versions of the academic template for hugo show this feature. For example, https://anakarinarm.github.io/en/ , what would it take to add this feature here?

[tlienart]

adding a dark/light switch requires:

• some javascript linked with a button, for instance adding a class 'dark' to objects with a class 'theme'
• a lot of CSS specifying what should happen to different divs if they're combined with 'dark'

I'm happy to give a hand to someone starting a PR on this but will not start this myself (similar reasoning as #9).

Ps:

• here's a cleaner example of a dark switch: https://fredrikekre.se/
• JS code https://fredrikekre.se/libs/hello-hermit.js (could probably be simplified)

Here's a reasonably well explained tutorial: https://dev.to/ananyaneogi/create-a-dark-light-mode-switch-with-css-variables-34l8