Why does this CSS margin-top style not work?

Question

I try to add margin values on a div inside another div. All works fine except the top value, it seems to be ignored. But why?

What I expected:
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Answer 1

Doesn't answer the "why" (has to be something w/ collapsing margin), but seems like the easiest/most logical way to do what you're trying to do would be to just add padding-top to the outer div:

http://jsfiddle.net/hpU5d/1/

Minor note - it shouldn't be necessary to set a div to display:block; unless there's something else in your code telling it not to be block.