<br> is an empty tag. Empty tags have no closing tag and no content.

Put together the line break tag.

<body>
<h1>My favorite things</h1>
<p>
Raindrops on roses<br>
Whiskers on kittens<br>
Bright copper kettles<br>
Warm woolen mittens
</p>
</body>
</html>
]]>

<br> doesn't need a closing tag.