For some reason, I get no autocomplete on html and css files. All works well with other languages, for example JS, Ruby or Python. I\'ve spent close to 2h today trying to fix it
I would suggest you use NeoComplete. I tried YouCompleteMe on Vim8, but doesn't work for some reason. NeoComplete does the job for me.
After installing NeoComplete just add, let g:neocomplete#enable_at_startup = 1 to your .vimrrc
let g:neocomplete#enable_at_startup = 1