php

 <?php
if (isset($_POST['submit'])) {
    if (!isset($_SESSION['username'])) {
        echo "<script>
           alert('Please Login')
       </script>";
       }
    else {
       echo "
          <script>
             $(document).ready(function(){
              $('button').click(function(){
             $('#service').slideToggle();
               });
             });
           </script>";}
    }



?>

<form action="" method="post">
    <input type="submit" name="submit" value="خدماتنا">
</form>


<div class="der  " id="service">
 <br><br><br><br>
 <a href="sell.html" target=_blank ><img src="sell.jpg" alt="Avatar" class="av" ></a>
 <a href="sellthing.html" target=_blank><img src="img.png" alt="Avatar" class="av" ></a>

 <a href="rent.html" target=_blank> <img src="img.png" alt="Avatar" class="av" ></a>
 <a href="rentthing.html" target=_content><img src="img.png" alt="Avatar" class="av" ></a>
   <br><br><br>
 </div>