I'm new to docker and I'm setting up a CodeIgniter docker image on my local machine bitnami/codeigniter:3

Everything works fine but the mysql container loses its DB and all the data every time I perform sudo docker-compose down

This is docker-compose file

version: '3.3'
services:
 myapp:
  image: docker.io/bitnami/codeigniter:3
  container_name: app-backend
  ports:
   - '8000:8000'
 volumes:
   - '.:/app'
depends_on:
  - mariadb
mariadb:
 image: docker.io/bitnami/mariadb:10.3
 container_name: app-marriadb
 volumes:
   - app_dbdata:/var/lib/mysql
 environment:
   MYSQL_ROOT_PASSWORD: root
   MYSQL_DATABASE: app_db
 ports:
   - '3307:3306'
 environment:
   - ALLOW_EMPTY_PASSWORD=yes
volumes:
 app_dbdata:

I tried multiple possibilities, but not sure where I'm going wrong. My OS is Ubuntu 18.04