That's odd - just to sanity check, I've taken just that bit of css and put it into a mini html document, it it behaves as expected:
Code:
<html>
<head>
<style type="text/css">
#mainWrapper {
background-color: #FFFFFF;
text-align: left;
width: 90%;
vertical-align: top;
}
body {
margin: 0;
font-family: verdana, arial, helvetica, sans-serif;
font-size: 62.5%;
color: #666666;
background-color:#000000;
}
</style>
<body>Hello
<div id="mainWrapper">Hello2</div>
</body>
</html>
and if you add margin: auto; you get the effect of a border all round:
Code:
<html>
<head>
<style type="text/css">
#mainWrapper {
background-color: #FFFFFF;
text-align: left;
width: 90%;
margin: auto;
vertical-align: top;
}
body {
margin: 0;
font-family: verdana, arial, helvetica, sans-serif;
font-size: 62.5%;
color: #666666;
background-color:#000000;
}
</style>
<body>Hello
<div id="mainWrapper">Hello2</div>
</body>
</html>
Is this the effect that you want?