CSS: Margin-top when parent's got no border

Question

As you can see in this picture, I've got an orange div inside a green div with no top border. The orange div has a 30px top margin, but it's also pushing the green div down. Of course, adding a top border will fix the issue, but I need the green div to be top borderless. What could I do?

.body {
border: 1px solid black;
border-top: none;
border-bottom: none;
width: 120px;
height: 112px;
background-color: lightgreen;
}

.body .container {
background-color: orange;
height: 50px;
width: 50%;
margin-top: 30px;
}

<div class="header">Top</div>
<div class="body">
<div class="container">Box</div>
</div>
<div class="foot">Bottom</div>

Answer 1

You could add overflow:auto to .body to prevent margin-collapsing. See http://www.w3.org/TR/CSS2/box.html#collapsing-margins