Any time you want to change your page 9 out of ten times it's done with javascript. Advise you to start studying. Js is used below
Code:
<body>
<div id="container">
<div id="bot1"></div>
<div id="top1" onclick="goAway();"></div>
</div>
<script type="text/javascript">
function goAway()
{
document.getElementById("top1").style.display = "none";
}
</script>
</body>
</html>
Just replace your code with this from the body tag down.