logout.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=
    , initial-scale=1.0">
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">
    <title>Blockchain</title>
</head>
<body>
    
    <div class="jumbotron jumbotron-fluid" id="new">
        <div class="container">
            <div class="alert alert-success" role="alert">
                Logout Successfull!
            </div>
            <p style="text-align: center">Please wait for few seconds...</p>
            
        </div>
    </div>

    <style>
        #new{
            position:fixed;
            top: 50%;
            left: 50%;
            width:30em;
            height:13em;
            margin-top: -9em; /*set to a negative number 1/2 of your height*/
            margin-left: -15em; /*set to a negative number 1/2 of your width*/
            border: 1px solid #ccc;
            background-color: #f3f3f3;
        }
    </style>
    <script>
        setTimeout(function(){
            location.replace('index.html'); 
        }, 5000);
    </script>
</body>
</html>