Add dark mode theme functionality and add its button on navbar

[Adarsh-K21]

[ranaji038]

i want to work on this issue

[Adarsh-K21]

assigned

[ayush-jain-09]

@Adarsh-K21 sir please assign to me

[Adarsh-K21]

@ayush-jain-09 assigned

[ayush-jain-09]

@ranaji038 bro, can u tell me what difficulties u faced during this task