Describe the bug

expect to output assets/index.css after building, but assets/style.css is created, the config is below:

{
    build: {
      cssCodeSplit: false,
      rollupOptions: {
        output: {
          manualChunks: undefined,
          assetFileNames: 'assets/[name][extname]',
          entryFileNames: 'assets/[name].js',
          format: 'iife'
        }
      }
    }
}

Reproduction

https://github.com/fengxinming/vite-plugins/tree/main/examples/demo

System Info

System:
   OS: Windows 7 6.1.7601
   CPU: (4) x64 AMD A10-7800 Radeon R7, 12 Compute Cores 4C+8G
   Memory: 2.78 GB / 6.96 GB
 Binaries:
   Node: 12.18.1 - C:\Program Files\nodejs\node.EXE
   Yarn: 1.22.10 - ~\AppData\Roaming\npm\yarn.CMD
   npm: 6.14.4 - C:\Program Files\nodejs\npm.CMD
 Browsers:
   Chrome: 91.0.4472.164
   Internet Explorer: 9.0.8112.16737

Used Package Manager

pnpm

Logs

No response

Validations

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• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to https://github.com/vuejs/vue-next instead.
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• The provided reproduction is a minimal reproducible example of the bug.