PHP registration

<!DOCTYPE html><html lang="en"><title>Test</title><meta name="viewport" content="width=device-width, initial-scale=1.5"><style>html{font-family:corbel; background:#ec9;}body,p,input,h1,h2,h3{padding:0.3em;margin-left:1em;color:#930;background:#dfe;}</style>
<?php
//3.php
//aera23@protonmail.com
echo'<p style="padding:1.2em;background:#ff8"><a href="4.php">There is a login page</a></p>';
echo '<h1>Welcome :)</h1><p>
<form action="4.php" method="post">
Use the tab keys to speed up form-filling.<br>
<input name="cn" placeholder="Nick" value="'.$_POST['cn'].'"><br>
<input name="ws" required placeholder="Code" value="'.$_POST['ws'].'"><br>
<input name="sx" required placeholder="Security">
<br><input type="submit" value="Save"><br>

Or hit enter.</p></form><p>If you lose your password, you\'ll need to confirm your "security".</p>';
?>