public function toOptionArray() {
        return [
            [
                'value' => self::BUTTON_BLACK,
                'label' => __('Black')
            ],
            [
                'value' => self::BUTTON_WHITE,
                'label' => __('White')
            ],
            [
                'value' => self::BUTTON_WHITE_LINE,
                'label' => __('White with line')
            ],
        ];
    }