如图效果:

先看看XHTML代码：

 
 
Item one 
 
Subitem one
 
Subitem two
 
Subitem three
 
Subitem four
 
 
 
Item two
 
Item three
 
Item four
 
 

看看CSS是如何定久相关元素的：

#navcontainer { margin-left: 30px; } 
#navcontainer ul 
{ 
margin: 0; 
padding: 0; 
list-style-type: none; 
font-family: verdana, arial, Helvetica, sans-serif; 
} 
#navcontainer li { margin: 0; } 
#navcontainer a 
{ 
display: block; 
padding: 5px 10px; 
width: 140px; 
color: #000; 
background-color: #ADC1AD; 
text-decoration: none; 
border-top: 1px solid #fff; 
border-left: 1px solid #fff; 
border-bottom: 1px solid #333; 
border-right: 1px solid #333; 
font-weight: bold; 
font-size: .8em; 
background-image: url(images/vertical06.jpg); 
background-repeat: no-repeat; 
background-position: 0 0; 
} 
#navcontainer a:hover 
{ 
color: #000; 
background-color: #889E88; 
text-decoration: none; 
border-top: 1px solid #333; 
border-left: 1px solid #333; 
border-bottom: 1px solid #fff; 
border-right: 1px solid #fff; 
background-image: url(images/vertical06a.jpg); 
background-repeat: no-repeat; 
background-position: 0 0; 
} 
#navcontainer ul ul li { margin: 0; } 
#navcontainer ul ul a 
{ 
display: block; 
padding: 5px 5px 5px 30px; 
width: 125px; 
color: #000; 
background-color: #C5D8C5; 
text-decoration: none; 
font-weight: normal; 
} 
#navcontainer ul ul a:hover 
{ 
color: #000; 
background-color: #889E88; 
text-decoration: none; 
}