Editor Form Buttons Class Override.

I'm using Bootstrap 4, the latest Datatables (from CDN) and Editor.

I'm having a problem overriding the classes for the form buttons that appear in the dialog. For example, I have:

{   extend: 'edit',
    editor: _this.main_editor,
    formTitle: "Update Opportunity",
    className: "btn btn-primary",
    formButtons: [
        {
            label: 'Update Opportunity',
            className: 'btn btn-primary',
            action: function () { this.submit(); }
        },
        {
            label: 'Cancel',
            className: 'btn btn-secondary ',
            action: function () { this.close(); }
        }
    ]
}

Yet the form buttons render as

<button class="btn btn-outline-secondary btn btn-primary" tabindex="0">Update Opportunity</button>
<button class="btn btn-outline-secondary btn btn-secondary" tabindex="0">Cancel</button>

For the buttons related to the table itself: (create, edit, remove ), I can do this:

buttons: {
    dom: {
        button: {
            tag: "button",
            className: ""
        }
    },

This removes the default classes and the buttons render with only the classes specified in className.

I cannot figure out how to achieve this for the form buttons.