How to change one element while hovering over another with CSS

I have looked at several other questions but I can't seem to figure any of them out, so here is my problem: I would like to have a div or a span, when you hover over it an area would appear and would be like a drop down.

Such as I have an div, and I want to hover over it and have it show some info about the item I hovered over

<html>
<head>
<title>Question1</title>
<styles type="css/text">

  #cheetah {
      background-color: red;
      color: yellow;
      text-align: center;
  }

  a {
      color: blue;
  }

  #hidden {
      background-color: black;
   }

   a:hover > #hidden {
      background-color: orange;
      color: orange;
  }
</styles>

</head>
<body>
  <div id="cheetah">
     <p><a href="#">Cheetah</a></p>
  </div>
  <div id="hidden">
     <p>A cheetah is a land mammal that can run up 2 60mph!!!</p>
  </div>
</body>
</html>

But this ^ doesn't seem to work, I don't know why... and if there is a way to do that in CSS, I would like to know, but I want any and all suggestions.

Solution

You can achieve this in CSS only if the hidden div is a child of the element you use for hovering:

http://jsfiddle.net/LgKkU/