Add dark mode

[Petrosdevri]

I think it would be useful to add the option for dark mode. We can do it by creating a button and using CSS to define classes for font colours.

[prrajakta]

@khushi2706 can you please allow me to add dark mode (if this issue is still pending)

[Anas-Nirban]

Hi @khushi2706,

As discussed earlier via email, my group has started to work on our open-source project for the college. Kindly assign us the issue so we can merge and complete our open source project.