Setting teh style for error returns and success returns

https://mdbootstrap.com/components/bootstrap-contact-form/Hellowhat 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: $email \r\n";mail($recipient, $subject, $content, $mailheader) or die("Error!");print json_encode(array('message' => 'Registration successful !', 'code' => 1));exit();?>

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