Mobile first, responsive with pure CSS

I don't use SASS or other preprocesser, because for the "newbies" the most important is dominant the basics of lenguajes (and because i don't know use it yet xD)

I try to do this responsive, and i said "try" because i think there are better methods than i use in this case, if you know how to better i'll thank give me feedback <3

My bigest problem was the background with the position background and the porcents, that made me write a media querye for each misalignment, and repeat code for change a single value :/

All other, if you see something you think can do better, please write it!

Be severe, is the way to learn. Thanks!

(Sorry if my english make you cry, i'm learning)