To make the border appear, we set the value to solid.

<html>
<head>
<style>
.coupon {
border: solid;}
</style>
</head>
<body>

<h2>Rainforest Online Shop</h2>

<p class="coupon">25% Discount Code: LST38151*</p>

<p>*This offer is subject to change without any prior notice.</p>

</body>
</html>]]>

Make sure to type solid.