Set the margin property to 50px.

<html>
<head>
<style>
p {margin: 50px;border: solid;text-align: center;}
</style>
</head>
<body>
<h1>Purchase confirmed!</h1>
<p>Thanks for shopping with Zbay!</p>


</body>
</html>]]>

Make sure to pick margin, followed by :, and finally 50px.