Better use two classes. And call a function, do not write an inline code. And use
onclick
Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>Untitled Document</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta http-equiv="Content-Style-Type" content="text/css">
<meta http-equiv="Content-Script-Type" content="text/javascript">
<style type="text/css">
#content.hidden{
display:none;
}
#content.shown{
display:block;
}
</style>
<script type="text/javascript">
function showhide(id){
var div=document.getElementById(id);
div.className=div.className=='hidden'?'shown':'hidden';
}
</script>
</head>
<body>
<a href="#" onclick="showhide('content');return false">Contest Rules</a>
<br>
<br>
<div id="content" class="hidden"> Content</div>
</body>
</html>