yaml: line 8:did not find expected key

these are my first times with docker, I'm trying to put the directives for MariaDB in my composer file. Once the file is written, if I try to run the docker compose up command, it gives me the following error: yaml: line 8: did not find expected key. Does anyone have the same problem as me? How can I solve? Thanks so much.

Below is my docker-compose.yaml file

version: '3'
    services:
      backend:
        build: ./
        restart: always
        volumes:
          - ./application:/var/www/html
        ports: [80:80]
       mariadb:
        image: 'bitnami/mariadb:latest'
        ports:
            - '3306:3306'
        volumes:
            - './mariadb_data:/bitnami/mariadb'
        environment:
            - ALLOW_EMPTY_PASSWORD=yes
            - MARIADB_DATABASE=db_test
            - MARIADB_USER=test_user
            - MARIADB_PASSWORD=password
            - MARIADB_ROOT_HOST='%'
    volumes:
      application:
        driver: local
      mariadb_data:
        driver: local

It happens when we do our own yml file for docker, you need to indent two spaces for sub entries under image details:

version: '1'
services:
    mariadb-ikg:
      image: bitnami/mariadb:10.3
      ports:
        - 3306:3306
      volumes:
        - D:/docker/bitnami-mariadb/databases:/bitnami/mariadb
      environment:
        - MARIADB_ROOT_PASSWORD=123456
    phpfpm-ikg:
      image: wyveo/nginx-php-fpm:php80
      ports:
        - 80:80
      volumes:
        - D:/docker/wyveo-nginx-php-fpm/wordpress:/usr/share/nginx/html
      depends_on:
        - mariadb-ikg