Making separate files for css and javascript and linking them to `index.html` file

**Is your feature request related to a problem? Please describe.**
CSS and JavaScript are written in the same file which is not a good way while developing a website.

**Describe the solution you'd like**
I want to make separate files for them and link them to the `index.html` file.

**Describe alternatives you've considered**
None

**Additional context**
Kindly assign it to me as part of hacktoberfest and web dev team of Hack4Bengal 2.0