<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
<style>
div:only-child {
color: #8ebf42;
font-weight: bold;
}
div {
display: block;
margin: 6px;
padding: 5px;
outline: 1px solid #1c87c9;
}
div div {
display: inline-block;
}
</style>
</head>
<body>
<h2>:only-child selector example</h2>
<div>
<div>I am an only child.</div>
</div>
<div>
<div>I am the 1st sibling.</div>
<div>I am the 2nd sibling.</div>
<div>
I am the 3rd sibling,
<div>but this is an only child.</div>
</div>
</div>
</body>
</html>