Invisible/white blocs, problem

So I’m trying to create site in Blocs that has grey(or any other) coloured blocs. Everything looks nice in the app. But when I export site and upload it (or preview in the browser) the blocks become white/transparent. I checked style.css and html files, everything looks right there. Tried to delete browser’s cache files. I don’t know what to do. I have tried almost everything now.

Anyone has solution for this?