Base Apparel Coming Soon | Responsive Grid Layout

Do you guys any idea of how I could make the form input more reausable?(A more appropriate class name etc).

Did I use the main element right? Or would it be better to use a section?

I used max-width: 300px for very small screens like the galaxy fold. Would it be better to start styling for small screens like that and then go on for bigger ones? I thought that as it was just a few lines of code it is okay.