I've been looking for this in google and it says that the css code is margin: 0 auto;. I tried it and it doesn't work for me. Please help. Thanks in advance. 
login.html
<html>
<head>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Log In</title>
 <link rel="stylesheet" type="text/css" href="stylesheet.css" />
</head>
<body>
 <div id="formLogin">
    <table class="formTable">
        <tr>
            <td>Username: </td>
            <td> <input type="text" id="loginusername" name="loginusername"/>  </td>
        </tr>
        <tr>
            <td>Password: </td>
            <td> <input type="password" id="loginpassword" name="loginpassword"/>  </td>
        </tr>
    </table>
    <div align="center">
        <input type="submit" id="btnlogin" name="btnlogin" value="Log In"/>
        <input type="submit" id="btncancelogin" name="btncancelogin" value="Cancel"/>
    </div>
 </div>
</body>
</html>
stylesheet.css
table.formTable {
 margin-left: auto;
 margin-right: auto;
}
table.formTable td {
 padding: 8px;
}
#formLogin {
 width: 360px;
 background-color: #eeeeee;
 margin: 0 auto;
 padding: 20px;
 -moz-border-radius:    10px;
 -webkit-border-radius: 10px;
 border-radius:         10px;
}
 
     
     
     
    