Using postcss/svelte-preprocess to inject css js as stylesheet?

[socketopp]

Currently coding a third party widget in sveltejs with tailwindcss and using rollup.js to build.
My goal is to inject the css to the head with the js file.

I have seen people do the following using the rollup-plugin-postcss plugin.
However I cannot use that, do you guys have any suggestions how I can do that using svelte-preprocess?

postcss: {
  extensions: ['.css'],
  minimize: true,
  inject: {
    insertAt: 'top'
  }
}

I currently have this in my App.svelte file and would like the preprocessor to inject it into my .js file but I am having real problems in achieving this since the rollup-plugin-postcss is missing ESM support.

App.svelte

<style global>
  @import '../preflight.css';
  @tailwind components;  
  @tailwind utilities;
</style>

[socketopp]

@benmccann
sveltejs/sapper#699 (comment)

Do you have any suggestions on how I should proceed with this?