Ecco come rimediare
codice:
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Documento senza titolo</title>
<style>
#sx{
float:left;
}
p {
    margin: 0;
}
</style>
</head>

<body>
<div id="sx">
<p>Sinisttrs</p>
</div>
<div id="dx">
<p>destra</p>
</div>

<div id="sx">
Sinistra
</div>
<div id="dx">
destra
</div>
</body>
</html>