This reproduces a behaviour in Vite where PostCSS isn't applied to styles included via composes.

Steps to reproduce

1. Install dependencies & run app

npm install
npm run dev

2. Open app in browser and inspect dynamically added <style> tags

Expected result

I exect to see the styles I include with .foo via `composes: component from "./component.module.css" to be valid (with PostCSS plugins applied). Expected result:

 ._component_xs2hm_5 {
  color: red;
  color: var(--color-red);
 }

 ._component_xs2hm_5 ._nested-component-class_xs2hm_13 {
  width: 100%;
}

._foo_1mrk0_1 {
  color: blue;
  color: var(--color-blue);
}

._foo_1mrk0_1 ._nested-bar_1mrk0_7 {
  width: 100%;
}

Note that the styles in main.module.css are valid in that nesting has been deconstructed (by postcss-nested) and property fallbacks have been added (via postcss-preset-env + importFrom).

Actual result

The styles included via composes are not processed by PostCSS. They are included in the <style> tag as-is, resulting in invalid CSS.

 ._component_xs2hm_5 {
  color: var(--color-red);

  ._nested-component-class_xs2hm_13 {
    width: 100%;
  }
}

._foo_1mrk0_1 {
  color: blue;
  color: var(--color-blue);
}

._foo_1mrk0_1 ._nested-bar_1mrk0_7 {
  width: 100%;
}

(I believe the class names of the composed class are transformed because in this reproduction I also import component.module.css separately in index.jsx).

The same bug can be observed in the production build.