Untitled

<!DOCTYPE HTML>
<html>
<head>
<style>
 form {

    margin: 0 auto;
    width: 400px;
    padding: 1em;
    border: 1px solid #CCC;
    border-radius: 1em;
    }

    form div + div {
    margin-top: 1em;
    }

    label {
    display: inline-block;
    width: 90px;
    text-align: right;
    }

    input, textarea {
    font: 1em sans-serif;

    width: 300px;
    box-sizing: border-box;

    border: 1px solid #999;
    }

    input:focus, textarea:focus {
    border-color: #000;
    }

    textarea {
    vertical-align: top;

    height: 5em;
    }

    .button {
    padding-left: 90px;
    }

    button {
    margin-left: .5em;
    }
</style>
 <title>My test page</title>
</head>
<body>

<?php
if ($_POST){
    $error = array();
    if (empty($_POST["names"])) {
      $error['name1'] = "Name is required";
    }
    if (empty($_POST["first_name"])) {
      $error['first_name1'] = "First Name is required";
    }
    if (empty($_POST["user_mail"])) {
      $error['user_mail1'] = "Email is required";
    }
    if (filter_var($_POST["user_mail"], FILTER_VALIDATE_EMAIL)){

    }
    else{
      $error['user_mail2'] = "Email non valide";
    }
    if (empty($_POST["n°telephone"])) {
      $error['n°telephone1'] = "Telephone is required";
    }
    if (empty($_POST["user_message"])) {
      $error['user_message1'] = "message is required";
    }

  if (count($error)==0){
      header("location:succes.php");
      exit();
  }
  }

?>
        <form method="post" action="">
            <div>
                <label for="name">Nom :</label>
                <input type="text" name="names" required >
                <?php if(isset($error['name1'])) echo $error['name1'];?></span>
                <br><br>
            </div>
            <div>
                <label for="first_name">Prénom :</label>
                <input type="text" name="first_name" required>
                <?php if(isset($error['first_name1'])) echo $error['first_name1'];?></span>
                <br><br>
            </div>
            <div>
                <label for="sujet">Théme du mail</label>
                <select name="sujet" id="sujet">
                <option value = "theme_1">théme 1</option>
                <option value = "theme_2">théme 2</option>
                <option value = "theme_3">théme 3</option>
                <option value = "theme_4">théme 4</option>
                </select>
            </div>
            <div>
                <label for="mail">e-mail :</label>
                <input type="email" id="mail" name="user_mail" required>
                <?php if(isset($error['user_mail1'])) echo $error['user_mail1'];?>
                <?php if(isset($error['user_mail2'])) echo $error['user_mail2']; ?>
                <br><br>
            </div>
            <div>
                <label for="telephone">téléphone :</label>
                <input type="tel" id="telephone" name="n°telephone" required>
                <?php if(isset($error['n°telephone1'])) echo $error['n°telephone1']; ?>
            </div>
            <div>
                <label for="msg">Message :</label>
                <textarea id="msg" name="user_message" required></textarea>
                <?php if(isset($error['user_message1'])) echo $error['user_message1']; ?>
            </div>
            <div class="button">
                <button type="submit">Envoyer le message</button>
            </div>
        </form>
    </body>
</html>