RWD with BEM and Grid Layout used 1st time along with mobile first

1. I've used "BEM" and "Grid" layout first time, along with "mobile first approach"
2. Kindly review the code and let me know areas of improvement.
3. As I'm using "mobile first approach" first time; didn't find much helpful. Please let me know from your experiences is it good way to tackle RWD or starting with desktop first ? About BEM
4. I simply fell in love with BEM, it's like love at first site.
5. I've learnt React and Tailwind CSS, I feel BEM will help you to master both React & Tailwind CSS. It makes life so much easy Your feedback is always welcome, thanks in advance.

Kind Regards, Vikram