Four Card Section

I followed along with a random tutorial that brought me to this challenge out of happenstance. This is my 3rd(?) challenge in which I followed along with another dev and I learned a lot in regards to breaking down a project. My questions would be in regard in how he set up his code? He nested his CSS (which i didn't know you could do) would this be the recommended way if your just using vanilla HTML/CSS? is it just preference? Is it situational? My other question is SASS vs CSS this is my second time using SASS and I've enjoyed it. I'm wondering in terms of usability and learning curve, should I learn SASS in conjunction with CSS? Or should i learn Vanilla CSS properly and THEN utilize SASS? what are your thoughts? Do you prefer one over the other? or is it project based? I'm Also having issues with getting my repository to Vercel, if anyone has any suggestions please help a noob out, i assure the code works i've opened it locally but I'm breaking something when i link it to Vercel.