Order Summary Site using HTML and custom CSS

I don't have any formal training on what "good code" is supposed to look like, so my worry is that my code looks a 3 year old's grammar sounds. Ha.

If anyone has suggestions on "best practices" when it comes to code layout, that would be helpful. Should I group my CSS differently? Is there a better way to make my code readable? Any resources to read or watch would be welcomed as well.

Thanks!