Product Preview Card solution using plain old HTML and CSS Grid

Hello Everyone! First and foremost, english isn't my first language so please forgive me for any mispellings or grammatical errors. There's two questions that i asked myself during this project and i'd hoped that maybe someone could help me shine some light on theses matters.

1. Responsive Web Design seemed to be mandatory nowadays but, when starting a design, is it better to first build the mobile design and then add complexity toward the bigger resolutions (laptop, desktop, etc) or the other way around? I'm an aspiring front-end developper and my first thought is to make the mobile layout first because there's less space to cover which means less complexity which seems really reassuring to me but i'd like to hear your more experience views on the subject.

2. This is my second project on Frontend Mentor and i noticed that the HSL color system seems to be preferred. I wonder if there was any particular reason. I thought rgb, hex and hsl were favorted by some and others due to personal preferences but maybe there's a more technical explanation?

Again i'm sorry for my poor writing. And if you guys feel like giving any feedback whatsoever, i'll gladly hear about it. Have a nice day and happy coding to all!