Code goes to you active theme’s functions.php file:

function wpcfe_after_add_shipment_style_cb(){
    ?>
    <style>
        div.sidebar-fixed.position-fixed a {
            color: #007bff;
        }
        div.sidebar-fixed.position-fixed a.active { 
            color: #ffff; 
        }
    </style>
    <?php
}
add_action('wpcfe_after_add_shipment', 'wpcfe_after_add_shipment_style_cb');