Add Light-Dark mode

[prasoonk1204]

Currently the website has only dark mode, I would like to make a light mode interface for it and a toggle in the navbar to switch between them.

please assign it to me, so i can start the work.

also add gssoc-ext, hactoberfest-accepted and level (1/2/3 -- based on what you think is the difficulty of this task) labels.

[sambedan1]

i have a great knowledge about it please assign it to me