don't forget for .env

docker-compose.yml

version: '2'
services:
  wordpress:
    env_file: 
      - .env
    depends_on:
      - db
    image: wordpress:latest
    restart: always
    volumes:
      - ./wp-content:/var/www/html/wp-content 
    environment:
      WORDPRESS_DB_HOST: db:3306
      WORDPRESS_DB_PASSWORD: ${WORDPRESS_DB_PASSWORD}
    ports:
      - ${PORT}:80 # Expose http and https
      # - 443:443
    networks:
      - back
  db:
    env_file: 
      - .env
    image: mysql:5.7
    restart: always
    volumes:
       - db_data:/var/lib/mysql
    environment:
      MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}
    networks:
      - back
  phpmyadmin:
    env_file: 
      - .env
    depends_on:
      - db
    image: phpmyadmin/phpmyadmin
    restart: always
    ports:
      - ${PMA_PORT}:80
    environment:
      PMA_HOST: db
      MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}
    networks:
      - back
networks:
  back:
volumes:
  db_data: