How to add a class to a button in Yii2-export?

Question

Yii

Good afternoon. I'm using the Yii2-export extension . By default, the buttons created by the plugin have the class btn btn-outline-secondary. I am trying to insert the classes I need like this:

<?= ExportMenu::widget([
    'dataProvider' => $dataProvider,
    'dropdownOptions' => [
        'label' => 'Export',
        'class' => 'btn btn-primary btn-sm font-weight-bold',
        'icon' => '<i class="fas fa-external-link-alt icon-nm"></i>'
    ],
    'columnSelectorOptions' => [
        'icon' => '<i class="fas fa-list icon-nm"></i>',
        'class' => 'btn btn-primary btn-sm font-weight-bold',
    ],
    'exportConfig' => ...
    'columns' => ...
]); ?>

But in the end, the extension renders this:

<button id="w4-button" class="btn btn-primary btn-sm font-weight-bold btn-outline-secondary dropdown-toggle" title="Export data in selected format" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"><i class="fas fa-external-link-alt icon-nm"></i> Эскпортировать</button>

That is, my classes were simply added to the beginning and overwritten by the default classes. How can I remove these classes by default?

I understand that the question is quite specific, but maybe someone used this plugin and faced such a problem.

*There doesn't seem to be a fix for this. I found this line in the source code

Html::addCssClass($this->dropdownOptions, ['btn', $this->getDefaultBtnCss()]);

That is, standard classes will always be added.