How to add slideDown animation in php bootstrap alert

How to add slideDown animation in php bootstrap alert

In my code, bootstrap alert is showing without any animation. I want to add jquery slideDown effect to error.

Error occurs when a user enters wrong credentials to log in. The server-side language is PHP

Here is my code.


<?php
include("includes/connect.php");
if(isset($_POST['submit'])){
$uname=$_POST['user'];
$user_pass=$_POST['pass'];
$query="select * from login_info where user_name = '$uname' AND password='$user_pass'";
$run=mysqli_query($conn,$query) or die("error");

if(mysqli_num_rows($run)>0){
$_SESSION['user_name']=$uname;
echo " <script>window.open( 'index.php', '_self') < /script>";
}
else{
echo '
<div class= "alert alert-danger" >
<a href= "#" data-dismiss= "alert" class= "close" aria-label= "close" ></a>
<strong>Error! </strong> Email OR Password is incorrect.
<a href= "#" class= "close" id= "btn" >&times; </a>
</div>
'
;
}
}

?>