Setting teh style for error returns and success returns

https://mdbootstrap.com/components/bootstrap-contact-form/ Hello what is the best way to set different styles for successful php returns and error returns.   <a class="btn btn-primary" onclick="validateForm()">Send</a> <div class="alert hide" role="alert hide"> <div class="status" id="status"></div> </div> .errorCSS { background-color: red; } .successCSS { color: #004085; background-color: #cce5ff; border-color: #b8daff; }     function validateForm() { $.ajax({ url : "register.php", type: "POST", data :$('#registration-form').serialize(), success: function(data, textStatus, jqXHR) { $('#status').text(data.message).addClass('successCSS'); if (data.code) //If mail was sent successfully, reset the form. $('#registration-form').closest('form').find("input[type=text], textarea").val(""); }, error: function (jqXHR, textStatus, errorThrown) { $('#status').text(jqXHR).addClass('errorCSS'); } }); }   <?php $firstname = $_POST['firstname']; $surname = $_POST['surname']; $email = $_POST['email']; header('Content-Type: application/json'); if ($firstname === ''){ print json_encode(array('message' => 'firstname cannot be empty', 'code' => 0)); exit(); } if ($surname === ''){ print json_encode(array('message' => 'Surname cannot be empty', 'code' => 0)); exit(); } if ($email === ''){ print json_encode(array('message' => 'Email cannot be empty', 'code' => 0)); exit(); } else { if (!filter_var($email, FILTER_VALIDATE_EMAIL)){ print json_encode(array('message' => 'Email format invalid.', 'code' => 0)); exit(); } } $content="Email: $email nMessage: $message"; $recipient = "@gmail.com"; $mailheader = "From: $email rn"; mail($recipient, $subject, $content, $mailheader) or die("Error!"); print json_encode(array('message' => 'Registration successful !', 'code' => 1)); exit(); ?>  

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