presentations/drupal/web/sites/default/environments/settings.docksal.php

<?php

$databases['default']['default'] = [
  'driver' => 'mysql',
  'host' => 'db',
  'database' => getenv('MYSQL_DATABASE'),
  'username' => getenv('MYSQL_USER'),
  'password' => getenv('MYSQL_PASSWORD'),
];

$settings['container_yamls'][] = __DIR__ . '/services.docksal.yml';