Adding dark mode to the website

[VamsiVD]

Please verify the following:

• This issue is related to the Mobile Interns First Steps document or myPlanet User Manual.
• You have searched for relevant keywords in recent open and closed issues to avoid duplicates.

URL to the MDwiki page containing the problem

https://open-learning-exchange.github.io/#!index.md

Problem

Eye Strain, Accessibility Issues. Doesn't offer the modern viewing experience users expect.
plus dark mode is superior

Screenshots (when necessary)

No response

Proposed solution(s)

Add
[gimmick:themechooser](Choose Theme)