使用css分層疊加元素

我一直在玩這個滑動下拉式jquery菜單。我將下拉區域上移一點，並帶有負邊界。我希望有一種方法可以在父元素上層疊下拉菜單，這是操作的觸發器。我試過z-index但沒有運氣。任何人都知道我在做什麼錯了？使用css分層疊加元素

這活：爲http://daveywhitney.com/overlay/sliding_menu.html

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml"> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 
<title>Sliding Menu Tutorial | HV-DESIGNS.CO.UK</title> 
<link href="style.css" rel="stylesheet" type="text/css" /> 
<script type="text/javascript" src="js/jquery.js"></script> 
<script type="text/javascript" src="js/slider.js"></script> 

</head> 

<body> 
<div id="container"> 
<div id="header"> 
</div> 

<div id="button"> 
<div id="trigger"> 
<img src="images/button.png" width="184" height="32" class="menu_class" /> 
</div> 
<ul class="the_menu"> 
<li><a href="#">A Website #1</a></li> 
<li><a href="#">A Website #2</a></li> 
<li><a href="#">A Link #1</a></li> 
<li><a href="#">A Link #2</a></li> 
<li><a href="#">A Website #3</a></li> 
<li><a href="#">A Website #4</a></li> 
<li><a href="#">A Link #3</a></li> 
<li><a href="#">A Link #4</a></li> 
</ul> 
</div> 

</div> 
</body> 
</html> 

body { 
    font-family:Arial, Helvetica, sans-serif; 
    font-size:12px; 
    background-color: #333333; 
} 

#container { 
    margin: auto; 
    width: 490px; 
} 

#header { 
    background-image: url(images/header.png); 
    background-repeat: no-repeat; 
    height: 42px; 
    width: 490px; 
    margin-bottom: 20px; 
} 

#button { 
    height: 32px; 
    width: 184px; 
    margin: auto; 
} 

ul, li { 
    margin:0; 
    padding:0; 
    list-style:none; 
} 

.menu_class { 
    border:1px solid #1c1c1c; 

} 
#trigger { 
    z-index:-1; 
} 
.the_menu { 
    display:none; 
    width:300px; 
    border: 1px solid #1c1c1c; 
    margin:-50px 0 0 50px; 
    z-index:100; 
} 

.the_menu li { 
    background-color: #302f2f; 
} 

.the_menu li a { 
    color:#FFFFFF; 
    text-decoration:none; 
    padding:10px; 
    display:block; 
} 

.the_menu li a:hover { 
    padding:10px; 
    font-weight:bold; 
    color: #F00880; 
}

來源

2011-03-20 Davey