Please merge my PRs.

[Megha-Chakraborty]

Hi GSSoC Team,
I pulled 3 requests, got respone for 1 but rest 2 are not merged yet. Please merge my Pull Request.
They're listed below.

1. Added dark and light mode in main.ing Ramsey99/fest-registration#104
2. Changes made in html file Shreyaa173/Code-Book#484

Thank you!
It was a great event, I learnt a lot.