Docker Compose for WordPress with theme mapped (example for my blog)

docker-compose.yml

version: '3.3'

services:
   db:
     image: mysql:5.7
     volumes:
       - db_data:/var/lib/mysql
     restart: always
     environment:
       MYSQL_ROOT_PASSWORD: somewordpress
       MYSQL_DATABASE: wordpress
       MYSQL_USER: wordpress
       MYSQL_PASSWORD: wordpress

   wordpress:
     depends_on:
       - db
     image: wordpress:latest
     volumes:
       - /Users/cdevroe/Sites/wordpress_themes/cypress/dist:/var/www/html/wp-content/themes/cypress
     ports:
       - "8000:80"
     restart: always
     environment:
       WORDPRESS_DB_HOST: db:3306
       WORDPRESS_DB_USER: wordpress
       WORDPRESS_DB_PASSWORD: wordpress
       WORDPRESS_DB_NAME: wordpress
volumes:
    db_data: {}

For those that want to map a local directory to one within the Docker container, look at the bit around Line 20.

volumes:
       - /Users/cdevroe/Sites/wordpress_themes/cypress/dist:/var/www/html/wp-content/themes/cypress

This maps my local directory to one within WordPress in the container. Every time I save my theme files they are immediately live within WordPress.