It depends, some solutions generate atomic css, some normal css rules, and a couple generate inline styles. CSS-in-JS is similar to React abstracting away HTML

It depends, some solutions generate atomic css, some normal css rules, and a couple generate inline styles. CSS-in-JS is similar to React abstracting away HTML, as well as solving global issues etc. React Native Web abstracts both the view and style layer, you work with a RN stylesheet based interface that generates atomic css on web and RN stylesheets on native. Similar to how React generates HTML on web and native controls on other platforms. Personally CSS is too bloated, I love working with a subset that includes flexbox and the core styling properties.