<ul class="tabnav el">
    <?php
    if ($_SERVER['SCRIPT_NAME']=='/plugins/TrustpilotAPI/admin/index.php') {
        $selected = ' class="selected"';
    } else {
        $selected = '';
    }
    ?>
  <li <?= $selected ?>>
     <a href="/plugins/TrustpilotAPI/admin/index.php">Login</a>
  </li>
</ul>