Shopware 6 Docker Setup add PHPMyAdmin

I am a totally beginner at Shopware and I want to use PhpMyAdmin for my local Shopware 6 setup.

For the download I used the official Shopware 6 Development repository https://github.com/shopware/development

I’ve already seen that the docker-compose.yml has implemented the following:

app_mysql:
    build: dev-ops/docker/containers/mysql
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_USER: app
      MYSQL_PASSWORD: app
    networks:
      shopware:
        aliases:
          - mysql

and now I want to implement phpmyadmin. I tried the following:

phpmyadmin:
      image: phpmyadmin/phpmyadmin
      links:
          - app_mysql:mysql
      depends_on:
          - app_mysql
      ports:
          - 8181:80
      environment:
          PMA_HOST: app_mysql
          MYSQL_ROOT_PASSWORD: root
          MYSQL_USER: app
          MYSQL_PASSWORD: app

phpmyadmin is visible on localhost:8181 but when I try to login I get the following errors:

mysqli::real_connect(): php_network_getaddresses: getaddrinfo failed: Name or service not known
mysqli::real_connect(): (HY000/2002): php_network_getaddresses: getaddrinfo failed: Name or service not known

How can I solve it?

Source: Docker Questions