Simple PHP Password Check

<?php

/**
* Very simple password protectetion for very simple php web pages
*/

$accessWord = 'nameOfMyGirlfriendOrDaughterWhereEsAreReplacedByThrees';

if (!isset($_COOKIE['accessWord']) || $_COOKIE['accessWord'] !== md5($accessWord)) {
    if (isset($_POST['accessWord']) && trim($_POST['accessWord']) === $accessWord) {
        setcookie('accessWord', md5($accessWord), time() + (7 * 24 * 3600));
    } else {
        echo '<meta charset="utf-8">';
        echo '<meta name="viewport" content="width=device-width, initial-scale=1">';
        echo '<style>';
        echo 'html { font-size: 20px; line-height: 1.5em; box-sizing: border-box; }';
        echo '*, *:before, *:after { box-sizing: inherit; }';
        echo 'input { font-size: 20px; line-height: 2.5em; padding: 0 0.5em; display: block; margin-bottom: 0.5em; }';
        echo 'input[type="submit"] { padding: 0.5em; }';
        echo '</style>';
        echo '<h1>Please enter accessword</h1>';
        echo '<form method="post" action="">';
        echo '<input type="password" name="accessWord" />';
        echo '<input type="submit" value="Send" />';
        echo '</form>';
        exit;
    }
}

// continue here the rest of your php code. Remove above when there is no need for password protection any longer
?>

<h1>Hi, welcome on my web site</h1>