HTML and CSS Structure

Structure of HTML page (foo.html):

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" ....>
<html .... >
<head>
....
</head>

<body>
....
</body>
</html>

Structure of a style sheet (foo.css):

body {
        background: pink;
        border: 4px solid black;
        ....
}
h1,h2,div,p,ul {
        ....
}
#top {
        ....
}
#sidebar {
        ....
}
#content {
        ....
}
#footer {
        ....
}