Legacy plugin inlines CSS

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Describe the bug

When attaching @vitejs/plugin-legacy, the index.css content is inlined into the index-legacy.[hash].js output file. This is reproducible with the base Preact template (and presumably others).

// index-legacy.[hash].js
var __vite_style__=document.createElement("style");__vite_style__.innerHTML="body,html{height:100%;width:100%;padding:0;margin:0;background:#fafafa;...",document.head.appendChild(__vite_style__) // ...`

truncated CSS for brevity

No changes/issues with the non-legacy output.

Reproduction

https://github.com/lukeed/bug-vite-legacy-inline-css

System Info

• vite version: 2.0.1
• Operating System: Mac OS
• Node version: 14.15.5
• Package manager (npm/yarn/pnpm) and version: pnpm 5.11.1

Logs (Optional if provided reproduction)

Don’t see anything useful within --debug output. Providing summary instead:

dist/assets/index-legacy.13201260.js       4.47kb / brotli: 1.82kb
dist/assets/vendor-legacy.14fe4df4.js      8.71kb / brotli: 3.26kb
dist/assets/polyfills-legacy.1b3a07f4.js   40.77kb / brotli: 14.08kb
dist/assets/favicon.17e50649.svg   1.49kb
dist/index.html                    1.09kb
dist/assets/index.e8186b7a.css     0.35kb / brotli: 0.17kb
dist/assets/index.2844346d.js      4.51kb / brotli: 1.87kb
dist/assets/vendor.cc9d1722.js     8.64kb / brotli: 3.27kb

[Bocom]

Would love an option to not have the CSS inlined in the legacy build since I’m integrating it in a backend-based project where I don’t have an index.html entrypoint to transform and thus enqueue the JS and CSS manually.

[Connum]

I would be willing to look into this and make a PR adding that option. But so far, I even fail to see where this inlining is happening - it doesn’t seem to come from vite or vite-plugin-legacy (unless I missed it). So it seems so happen in one of the dependencies? Any hint would be welcome!

Update: Ok, just a few seconds after posting this, I stumbled upon #4448 - this seems related and I know where to look further now. However, I think a fix should be found that covers both the issues, using the legacy plugin or not.