<?php $cl =$_REQUEST['cl']; ?>
<ul class="nav nav-pills flex-column flex-md-row mb-3">
        <li class="nav-item">
            <a class="nav-link <?php if($cl==22){    echo 'active';;} ?> "href="Attendance_teacher.php?cl=22"><i class="bx bx-user me-1"></i> Teacher </a>
        </li>
        <li class="nav-item">
            <a class="nav-link <?php if($cl==0){    echo 'active';;} ?> "href="class_teacher_attendance.php?cl=0"><i class="bx bx-user me-1"></i> Staff </a>
        </li>
</ul>