Env varibale for Vue Js Page for Github Action Firebase Deploy

Question

I am facing problem of providing env variable to my vuejs page for github action deploy. I have a remote dev branch and when I push to dev branch, github actions triggers and deploy using firebase. My page uses a backend url (process.env.backend_url) which I want to pass from yml file. And I cant figure out how.

This is my yml file for dev push.

name: Deploy to Firebase Hosting on  to Dev
'on':
  push:
    branches:
      - dev
jobs:
  build_and_deploy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-node@v1
        with:
          node-version: '14'
      - run: npm ci
      - run: CI=false npm run build:dev
      - uses: FirebaseExtended/action-hosting-deploy@v0
        with:
          repoToken: '${{ secrets.GITHUB_TOKEN }}'
          firebaseServiceAccount: '${{ secrets.FIREBASE_SERVICE}}'
          channelId: live
          projectId: projectid
          target: dev
        env:
          FIREBASE_CLI_PREVIEWS: hostingchannels