wordpress:
    ...
    container_name: OPTIONAL <-
    volumes:
      - ./themes/OPTIONAL:/var/www/html/wp-content/themes/OPTIONAL <-
    ...
    ports:
      - "8000:80" <-
    ...
    networks:
      - OPTIONAL_network <-
    ...

  db:
    ...
    container_name: OPTIONAL_db <-
    ...
    networks:
      - OPTIONAL_network <-
    ...

...

networks:
  OPTIONAL_network: <-

WORDPRESS_DB_NAME=wordpress
WORDPRESS_DB_USER=admin
WORDPRESS_DB_PASSWORD=password

MYSQL_RANDOM_ROOT_PASSWORD=yes
MYSQL_DATABASE=wordpress
MYSQL_USER=admin
MYSQL_PASSWORD=password

$ docker-compose up -d

$ docker exec wordpress_db /usr/bin/mysqldump -u admin --password=pass wordpress > wordpress.sql

$ docker-compose build