Question

Here’s a fiddle I setup illustrating the problem.

http://jsfiddle.net/rgfjL/13/

Here’s the code

HTML

<div class="body">
    <div class="contact-form" class="clearfix">
        <p> asdsasadsad </p>
    </div>
<div>

CSS

div.body {
  display: block;
  height: 800px;
  width: 1024px;
  background: #474747;
}

div.contact-form {
  display: block;
  background-color:#F2F7F9;
  height: 600px;
  width:465px;
  padding:20px;
  margin: 250px auto;
  border: 6px solid #8FB5C1;
 -moz-border-radius:15px;
 -webkit-border-radius:15px;
  border-radius:15px;
}​

As you can see in the fiddle, the form div is flush against the top of the body div. Changing top margin on form pushes both of them down.

Answer 1

Because this is Collapsing Margins

div.body {
    overflow: hidden;
 }

live demo http://jsfiddle.net/rgfjL/15/

more info http://reference.sitepoint.com/css/collapsingmargins