HTML5 & CSS: esempio base

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="it">
<head>
<title>HTML5 & CSS3: layout sito con 2 colonne</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<link type="text/css" rel="stylesheet" href="style.css" title="Style" media="all" />

<style type="text/css">

body {
    background:white;
    text-align:center;
    font-family:Helvetica, arial, sans-serif;
}

div#contenitore {
    background:#50b4ab;
    width:900px; margin:0 auto;
    text-align:left;

}

div#header {
    background:#92808b;
        text-align:center;
    height:5em;
        color:white;
        font-family:Verdana, serif;
}

h1 {
    color:white;
    text-align:right;
    padding:1em 1em 0 0;
    font-family:Georgia, serif;
}

h2  {
    color:white;
    text-align:right;
    padding:1em 1em 0 0;
    font-family:Georgia, serif;
}


div#colsx {
    width:630px;
    float:left;
    padding:10px;
    border-top:3px solid white;
}

div#coldx {
    background:#99c199;
    width:227px;
    float:left;
    padding:10px;
    border-left:3px solid white;
    border-top:3px solid white;
}

div#footer {
    background:#a3a3a3;
    clear:left;
    border-top:3px solid white;
    text-align:center;
}

</style>
</head>


<body>

    <div id="contenitore">
    <div id="header">LA TESTA DEL TUO SITO</div>
    <div id="colsx">
        <header><h1>QUESTA È LA COLONNA 1</h1></header>
            <article>« Lorem ipsum dolor sit amet, consectetur adipisici elit, sed eiusmod tempor incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat. Quis aute iure reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint obcaecat cupiditat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. »<article></div>

    <div id="coldx">
        <header><h2>QUESTA È LA COLONNA 2</h2></header>
            <article>« Lorem ipsum dolor sit amet, consectetur adipisici elit, sed eiusmod tempor incidunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquid ex ea commodi consequat. Quis aute iure reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint obcaecat cupiditat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. »</article></div>

    <footer><div id="footer">IL FOOTER DEL TUO SITO © 2007 Esmpio Inc.</div></footer>
</div>
</body>
</html>