Function resolveLibCssFilename

packages/vite/src/node/plugins/css.ts:3585–3605

(
  libOptions: LibraryOptions,
  root: string,
  packageCache?: PackageCache,
)

}

export function resolveLibCssFilename(
  libOptions: LibraryOptions,
  root: string,
  packageCache?: PackageCache,
): string {
  if (typeof libOptions.cssFileName === 'string') {
    return `${libOptions.cssFileName}.css`
  } else if (typeof libOptions.fileName === 'string') {
    return `${libOptions.fileName}.css`
  }

  const packageJson = findNearestMainPackageData(root, packageCache)?.data
  const name = packageJson ? getPkgName(packageJson.name) : undefined

  if (!name)
    throw new Error(
      'Name in package.json is required if option "build.lib.cssFileName" is not provided.',
    )

  return `${name}.css`
}