[FEATURE] Dark Mode for main landing page

[MitulSonagara]

Is your feature request related to a problem? Please describe.
no this is not a problem

Describe the solution you'd like
I would like to add dark mode button to main landing page

Describe alternatives you've considered
There is dark mode available for practice section of the typing test. But there is no dark mode for main page. So I would like to add dark mode button to main landing page.

I am contributing under CodePeak 2023