Add Dark Mode toggle button

[Hemashree21]

I want to work on designing the website in dark mode so that users can toggle between the mode of their choice.
@thestarsahil can you please assign this issue to me? I have also attached a template below.

[github-actions]

Hello Hemashree21, Thanks for opening an issue, your contribution is valuable to us. The maintainers will review this issue and provide feedback as soon as possible.

[thestarsahil]

Good to Go !