using rewrites does not include external css firebase

I use firebase.json to rewrite any request to /index.html which have link to external css in the same directory.
firebase.json:

"rewrites": [
  {
      "source": "**",
      "destination": "/index.html"
  }
]

However, when I go to sub url like example.com/user, the index.html the linked css did not imported. And the script resource also did not imported, instead console spit this error:

failed to load module script: expected a javascript module script but the server responded with a mime type of "text/html"

I searching in firebase docs, and find the header config that

Applies a CORS header

I did not understand, is this what I need ?
Do I need to use absolute path instead ?

I only use firebase hosting not cloud function. Any help would appreciated