Version

3.0.2

Steps to reproduce

1. Create a random single file vue component and use v-deep selector:

::v-deep(.selector) {
 color: red;
}

2. run npm run serve
3. See it works
4. Run npm run build
5. Selector is not working

What is expected?

new syntax of v-deep works correctly

What is actually happening?

new syntax of v-deep doesn't work correctly

Don't open issues without reproduction. Thanks. You can use https://github.com/vitejs/vite. I imagine you read the existing RFC as well: https://github.com/vuejs/rfcs/blob/scoped-styles-changes/active-rfcs/0023-scoped-styles-changes.md