feature : add a dark mode button

[Abhishekcpr]

Describe the solution you'd like
A dark mode button to be added in navbar which can be toggled so that user can switch from light mode to dark mode

[SanjanaSogimatt]

Can I work on this issue?

[sangwan-smriti]

i would like to work on this issue . also , @birm will i have to add UI for dark mode too?
or just add the button?

[sangwan-smriti]

i also faced the issue as i had to view website in dark mode which was not available