Nie mam pomyslu jak wysrodkowac odnosniki w menu, moze ktos pomoze?

oto kod:
<!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" lang="en" xml:lang="en"> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> <link rel="stylesheet" type="text/css" href="style.css" />
banner
<li> <a href="link1.php">Link1
</a> </li> <li> <a href="link2.php">Link2
</a> </li> <li> <a href="link3.php">Link3
</a> </li> <li> <a href="link4.php">Link4
</a> </li>
#strona
{
width: 900px;
margin: auto;
padding: 0px;
}
#banner
{
display: table-cell;
vertical-align: middle;
width: 900px;
height: 100px;
background-color: blue;
text-align: center;
}
#menu
{
width: 900px;
height: 50px;
background-image: url(grafika/menu.png);
}
#menu ul
{
list-style: none;
margin: 0px;
padding: 0px;
}
#menu ul li
{
float: left;
height: 50px;
width: 100px;
}
#menu a:link, #menu a:visited
{
height: 50px;
text-align: center;
text-decoration: none;
display: block;
background-image: url(grafika/menu2.png);
}
#menu a:hover
{
background-image: url(grafika/menu1.png);
}