Using a .cjs extension in the main field of package.json (e.g. "main": "./dist/foo.cjs") as per README causes microbundle to swallow any .css or .scss files imported

Reproduction steps

Repo: https://github.com/lokimckay-references/microbundle-883

1. npm init -y
2. npm install microbundle --save-dev
3. add styles.css and index.js files
4. import "./styles.css" within index.js
5. copy source/exports/main/module/unpkg fields into package.json as per README

   {
     "name": "foo",                     // your package name
     "type": "module",
     "source": "src/foo.js",            // your source code
     "exports": "./dist/foo.modern.js", // where to generate the modern bundle (see below)
     "main": "./dist/foo.cjs",          // where to generate the CommonJS bundle
     "module": "./dist/foo.module.js",  // where to generate the ESM bundle
     "unpkg": "./dist/foo.umd.js",      // where to generate the UMD bundle (also aliased as "umd:main")
     "scripts": {
       "build": "microbundle",          // compiles "source" to "main"/"module"/"unpkg"
       "dev": "microbundle watch"       // re-build when source files change
     }
   }
   

6. update source field to point to index.js
7. npm run build

Actual output

• All compiled formats of index.js
• Below error message

The emitted file "foo.cjs" overwrites a previously emitted file of the same name.

Expected output

• All compiled formats of index.js
• styles.css
• No error message

Workaround

Change the file extension of the main field from ./dist/foo.cjs -> ./dist/foo.js
= achieves expected output