flexboxgrid/meta/definitions.php

<?php

return [
    'assets.flexbox' => [
        'picea' => [
            'asset' => [
                'source' => [
                    [
                        'path' => implode(DIRECTORY_SEPARATOR, [ dirname(__DIR__), "asset", '' ]),
                        'order' => 10
                    ]
                ],
            ]
        ],
    ],
];