p:first-child background: moccasin;
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns='http://www.w3.org/1999/xhtml' xml:lang='en'>
<head>
<title>:first-child</title>
<style type='text/css'>
body {
font-size: 12px sans-serif;
}
p {
padding: 3px;
}
p:first-child {
background: moccasin;
border: 1px solid tan;
}
</style>
</head>
<body>
<p>
The selector applies to this element, because it is the
first child.
</p>
<p>
It does not apply to this element, because it is not the
first chld.
</p>
</body>
</html>