It is absolutely possible to re-use existing styles and themes.

The Material Compose theme adapter allows you to bridge your xml styles to compose. See: https://material-components.github.io/material-components-android-compose-theme-adapter/

It does assume that you've set up a theme base on Material Design. (Hence the library's name.) But you can absolutely re-use the M2 or M3 material design styles and is a great way to bridge an existing app's theme into compose rather than making a hard cut over. So your existing body1, body2, headline1 through 6 styles, etc are all re-usable. It will pull in the fonts you've set up, etc.

There's a version of the lib (https://github.com/google/accompanist/tree/main/appcompat-theme) for people who've gone the AppCompat theme route.

That's not to say that the bridge should be used long term. Eventually the theme should be moved fully to compose. But it is a good way to get started with compose and have the app themed correctly.