Set the height property to make all elements of the square class square-shaped.

<html>
<head>
<link rel="stylesheet" href="style.css">
<style>
.square {
height: 150px;
width: 150px;
background-color: teal;
}
</style>
</head>
<body>
<p class="square">A square has four equal straight sides and four right angles.</p>
</body>
</html>]]>

Make sure to pick 150px.