<html>
<header>
<style type="text/css">
div {
text-align:center;
margin:0 auto;
/* background-color: green; */
}
</style>
</header>
<body>
<div>
<form action="index.php" method="POST">
<input type="text" name="cifra1">+
<input type="text" name="cifra2">=
<input type="text" name="login"><br>
<input type="submit">
</form>
</div>
<?
?>
</body>
</html>