CSS not functioning. Need help :(

I've been using Jeden Desmonds google doc for most of my CSS work yet for some reason, when i tried to copy and paste some of the coding into it and edit it like usual nothing changes. I don't know what's wrong with it. Is it because of some sort of update or something? I work on a chromebook and just recently there was an automatic update but i'm not sure if it's cause of that and if so then it's a shame cause then i probably won't be able to edit my account any longer.
https://docs.google.com/document/d/1DbRQ-qscSPuS339NtijeLAL-W0Wmtmf5fuEhSo70nV8/edit
has anyone else experienced this issue? please message me if you know how to fix this. my gmail is humdrumramen@gmail.com
Is it like too much coding or paragraphs? What am i doing differently?