Bundle webcomponent.js with webcomponent.css

I have a pure vanilla webcomponent, lets call it "Spinner.js" and a "Spinner.css". Can I bundle this to just one JS-File including
the CSS file?.

Currently my rollup configuration looks like this, but CSS ins not bundle inside *.JS File
```
const bundle = await rollup({
input: `${webcomponent.pathToWebcomponent}`,
plugins: [nodeResolve(), commonjs(),postcss({
extract: false,
minimize: true,
inject: {
insertAt: 'top',
},
}), terser()],
})
```