Adding icon to button in admin orders page

Here is my plugin code to add a new button to the orders page:

function foo_add_my_action($actions, $the_order){
        /**
         * Merge arrays so that our button is first
         */
        $newActions = [];
        if($the_order->is_paid()){
            $newActions['myLink'] = array(
                'url' => plugin_dir_url( __FILE__ ) . 'somepage.php?bookId=' . $the_order->id,
                'name' => 'my link',
                'action' => 'my-link'
            );
        }

        return array_merge($newActions, $actions);
    }
    add_filter( 'woocommerce_admin_order_actions', 'foo_add_my_action', 10, 2);

And the css rule:

.my-link:AFTER{
    content: "\f227";
}

…results in a button (that works btw) with the text my-link and a square with F227 in it.