Here you go, this is my docker compose. You can modify the pieces as you see fit.

version: '3' services:

Bookstack

bookstack:
    image: lscr.io/linuxserver/bookstack
    container_name: bookstack
    environment:
        - PUID=${PUID}
        - PGID=${PGID}
        - APP_URL=
        - DB_HOST=bookstack_db
        - DB_USER=bookstack
        - DB_PASSWORD=${BS_DB_PASS}
        - DB_DATABASE=bookstackapp
    volumes:
        - ${DATA_DIR}/bookstack:/config
    ports:
        - 6875:80
    restart: unless-stopped
    depends_on:
        - bookstack_db
bookstack_db:
    image: lscr.io/linuxserver/mariadb
    container_name: bookstack_db
    environment:
        - PUID=${PUID}
        - PGID=${PGID}
        - MYSQL_ROOT_PASSWORD=${BS_DB_PASS}
        - TZ=${TIMEZONE}
        - MYSQL_DATABASE=bookstackapp
        - MYSQL_USER=bookstack
        - MYSQL_PASSWORD=${BS_DB_PASS}
    volumes:
        - ${DATA_DIR}/bookstack/mariadb:/config
    restart: unless-stopped