I started from "what the hell" to "what? why?" and now "😎yess"! Nonetheless, it was a worthwhile experience. It helped my understanding of CSS to mature. Mostly I used flexbox and some media queries to have that beautiful and seamless responsive layout.
I made sure to make the website responsive on every platform including Samsung Galaxy Fold and Microsoft Surface Duo.
Note: It has a problem with Samsung Galaxy S8+ in landscape orientation. The top side of the form gets hidden, I don't know the solution to it yet.
Author: The issue has been fixed. A simple media query on landscape orientation was sufficient for this slight re-adjustment.