Failed to fetch when dynamically importing css file after built

[zoubingwu]

Describe the bug

When dynamically import css files, it failed to fetch with built files being served.

It works in dev mode tho.

Reproduction

https://github.com/zoubingwu/vite-dynamic-import-css-bug

this repo was created thru yarn create @vitejs/app vite-dynamic-import-bug --template react-ts;

then simply run yarn add prismjs,

add few lines of code in App.tsx:

useEffect(() => {
    import('prismjs/themes/prism-coy.css')
    import('prismjs/themes/prism-dark.css')
    import('prismjs/themes/prism-funky.css')
    import('prismjs/themes/prism-okaidia.css')
    import('prismjs/themes/prism-solarizedlight.css')
    import('prismjs/themes/prism-tomorrow.css')
    import('prismjs/themes/prism-twilight.css')
    import('prismjs/themes/prism.css')
  }, [])

then run yarn build and yarn serve, you can find errors in console:

The css files were bundled,

But it requires js in the tranpiled code， and they are missing in the output:

System Info

Output of npx envinfo --system --npmPackages vite,@vitejs/plugin-vue --binaries --browsers:

  System:
    OS: Linux 5.8 Ubuntu 20.04.2 LTS (Focal Fossa)
    CPU: (8) x64 Intel(R) Core(TM) i7-8705G CPU @ 3.10GHz
    Memory: 1.33 GB / 23.41 GB
    Container: Yes
    Shell: 5.8 - /usr/bin/zsh
  Binaries:
    Node: 14.16.0 - ~/.nvm/versions/node/v14.16.0/bin/node
    Yarn: 1.22.10 - ~/.nvm/versions/node/v14.16.0/bin/yarn
    npm: 6.14.11 - ~/.nvm/versions/node/v14.16.0/bin/npm
  Browsers:
    Chrome: 90.0.4430.93
    Firefox: 88.0
  npmPackages:
    vite: ^2.2.3 => 2.2.4 

Used package manager:

yarn

Logs

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