Here I posted a demo http://jsfiddle.net/LxYMv/1/.
As you can see gets margin-top:10px from the top div, and therefor
You can get around this by adding padding: 0.01px; to the <body>. As it's so small it is effectively rounded to 0px, but the body then starts where it should.
padding: 0.01px;
<body>
0px