Dynamic require of "react" is not supported

I created a modal with createPortal, using react-dom, react and inline css. I get this error when running on a project. My config:

```ts
import { defineConfig } from 'tsup'

export default defineConfig({
entry: ['src/index.ts'],
format: ['cjs', 'esm'],
target: 'es2021',
splitting: false,
minify:true,
treeshake:true,
clean: true,
dts: true,
external:['react', 'react-dom']
})
```

Start with the provided tsup configuration and the src/index.ts entry point, then reproduce the modal build using both CJS and ESM formats. Inspect the generated output to identify why react is dynamically required despite being external, and consider the issue done when the build runs without this error.

Written by the indexing model from the issue text.