I'm looking for a ui system that is style agnostic... so I can use Bootstrap / Material UI / Tailwind CSS / custom css / etc.

From the docs, it looks like I can set custom classes. ex:
https://coreui.io/react/docs/4.1/components/accordion/#caccordionheader

className | A string of all className you want applied to the base component.

but elsewhere the docs say it extends bootstrap:
https://coreui.io/react/docs/4.1/getting-started/introduction/#stylesheets

@coreui/coreui library is compatible with bootstrap, it just extends its functionalities.

It isn't clear which it is:

1. className replaces the class name (only my styles are rendered)?
2. className extends the class name (and keeps bootstrap classes)?

thanks for your help!