Mi da errori ma non li vedo:

Line 28, Column 2: "DOCTYPE" declaration not allowed in instance.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"

Line 30, Column 66: document type does not allow element "html" here.
…tp://www.w3.org/1999/xhtml" xml:lang="it" lang="it">

Questo è il mio:

codice:
<!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="it" lang="it">
<head>
<meta http-equiv="content-type" content="text/html; charset=iso-8859-1" />
<script type="text/javascript" src="script.js"></script>
<style type="text/css" media="screen">@import url("css.css");</style>