Can you please tell me what mistakes I make when making layout?

Question

css

Point out the mistakes that I make when imposition. I'm new in this business. I taught for about 3 months. I want to know if I'm doing everything right.

Answer 1

ul {}
.about_us span{} 
footer {}

don't make such selectors. I want to add a span somewhere and it will have a margin
or the footer tag will be with a picture,
you can read about BEM