Blocks are not styled on frontend

Hello.
I started using Gutenberg editor and i encountered a problem. When i edit post/page i can add blocks and customize them (colors, formatting, etc). But when i try to preview it, those previously added blocks are not styled at all. I assume that on preview page those blocks should look the same as on edit page, shouldn’t they? Or that means that i need to add CSS by myself to each class, which Gutenberg generates for block? I suppose i just miss some configurations or something else, so blocks cannot be displayed correctly on a frontend page. Please tell me if i misunderstand how it should work