Best way to migrate to built-in CSS

[vitalybaev]

We have pretty big Next.js project with PostCSS styles in old manner - we simply import css files in components and use BEM name convention.
Now we want to switch to built-in CSS support (global stylesheets + modules in components). But we can't just start using it for some components, we have to refactor all of our components, migrating them to CSS modules. Am I right? Is there any way to achieve it with minimal effort?
Thanks