Please don't be intimidated by the work of others. It may seem that others are catching on more quickly than you are.
Many students come through this course to hone their existing CSS skills.
It is quite possible that these classmates have taken this class before. I have seen some students take this course three times. This class does cover all of CSS Level One. It is a lot of information. Take your time and you will understand it.
Some classmates may have other background in CSS. They may have read books or articles. They may have investigated CSS related websites. They may even have taken courses elsewhere on the internet or in a physical classroom.
Please do not shy away becasue someone else's work seems so much more advanced. You can learn from their examples.
Don't worry if their source code is showing unfamililar tags or constructions: You will learn about that in a future lesson.
If it is your first time learning CSS, please, PlEaSe, PLEASE concentrate on learning CSS. Don't worry about design. You can play with design next semester.