<style>
    .red {
        border: 1px solid red;
    }
</style>

<?php
ini_set("display_errors", 1);
error_reporting(E_ALL);
$name1 = "";
$text1 = "";
if (isset($_POST['name']) && isset($_POST['text'])) {
    $data = array_map("trim", $_POST);
    $data = array_map("strip_tags", $_POST);
    $name = $data['name'];
    $name1 = "Имя: ".$name;
    $text = $data['text'];
    $text1 = "Сообщение: ".$text;
    $submit = $data['submit'];
    $check = $data['check'];
}
if(empty($check)) { ?>
<form action="" method="POST">
    <span>Ваше имя:</span>
    <input type="text" name="name" value="<?php echo (isset($name))?$name:"" ?>" class="<?php echo (isset($submit) && empty($name))?"red":"" ?>">
    <span>Ваше сообщение:</span>
    <textarea rows="1" cols="25" name="text" class="<?php echo (isset($submit) && empty($text))?"red":"" ?>"><?php echo (isset($text))?$text:"" ?></textarea>
    <input type="hidden" name="check">
    <input type="checkbox" name="check" <?php echo (empty($check))?"":"checked"; ?>>
    <input type="submit" name="submit">
</form>
<?php
}
    echo $name1."<br>";
    echo $text1."<br>";
?>