Its a bit tricky to style with Gutenberg blocks. It often does not work just by adding custom styles through styles.css in a child theme. A WordPress Block Styles site created by WordPress theme team member Carolina Nymark is very handy valuable resource with tutorials & guides for style blocks designed for beginners.
Gutenberg block editor team member Riad Benguella has post at make.wordpress.org titled Controlling the Block Editor explaining how to extend block editor API to restrict, style variation, to restrict the content of Posts, Pages, CPTs to a given format with locked templates, theme support (eg colors, font sizes, gradients) third-party blocks with examples.