PHP - Header redirect issue Occur in Live Server

Method I
<?php
ob_start();
if(isset($_GET['elimina_id'])){
 if (in_array($_GET['elimina_id'], $_SESSION['cart']) ) {
  $index = (array_keys($_SESSION['cart'], $_GET['elimina_id']));
  $i = $index[0];
  unset($_SESSION['cart'][$i]);
  header('location: cart.php');
 }
}
ob_end_flush();
?> 


Method II
HTML: <meta http-equiv="refresh" content="0;url=http://www.site.com/cart.php">
JavaScript #1: <script>window.location = "http://www.site.com/cart.php";</script>
JavaScript #2: <script>window.navigate("http://www.site.com/cart.php");</script>

Set Position of Bootstrap Modal Popup

@media screen and (min-width: 768px) {
    .modal-dialog {
        left: 50%;
        right: auto;
        width: 624px;
    }
}
.modal-dialog{
position: absolute;
left: 50%;
//now you must set a margin left under zero - value is a half width your window
margin-left: -312px;
// this same situation is with height - example
height: 500px;
top: 50%;
margin-top: -250px;
} 

Alphanumeric Validation

Enter text filed only to allow alphabit & Numbers 
function alpha_numeric_validation(arg){
 var valReg = /^[A-Za-z0-9]+$/;
 if(valReg.test( arg ) ) {
  return false;
 } else {
  return true;
 }
}