docker-compose variable format

Question

I have the following docker-compose file. I have created the .env file as well with the relevant variables. when I attempt to run docker-compose using this file it complains about the variables. I know in Ansible yaml I declare the vars inside the file and can call them anywhere. Not sure what what I am doing wrong.

---
version: "3"
services:
  ${hostname01}:
    image:  apline:3.12
    restart: unless-stopped
    container_name: ${hostname01}
    environment:
    volumes:
      - ${hostname01}_Data:/var/www/html
    ports:
      - 80:80
      - 443:443
    
services:
  ${hostname02}:
    image: mariadb
    restart: unless-stopped
    environment:
      MYSQL_ROOT_PASSWORD: ${mySQLRootPass}
    volumes:
      - ${hostname02}_Data:/var/lib/mysql
    ports:
      - 3306:3306
volumes:
  ${hostname01}_Data:
  ${hostname02}_Data:
    driver: local

Answer 1

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