在左侧三级菜单导航想必大家都见到过吧，它的实现过程也并不复杂，下面有个不错的示例，感兴趣的朋友可以了解下
实例代码：
<!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" xml:lang="en" lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> <title>左侧三级菜单导航-www.jbxue.com</title> <style type="text/css"> <!-- body { font-family: Arial, Helvetica, sans-serif; font-size: 11px; } #nav, #nav ul { list-style: none; background: #F9F9F9; font-weight: bold; padding: 0px; margin: 0px; border: solid 1px #CCCCCC; border-bottom: 0px; 150px; text-align: left; } #nav ul ul{ border: solid 1px #CCCCCC; border-bottom: 0px; } #nav a { display: block; 150px; 140px; color: #333333; text-decoration: none; text-align: center; border-bottom: solid 1px #CCCCCC; text-align: left; padding-left: 10px; } #nav a:hover{ color: #336666; } #nav a.selected{ background: url(http://www.jbxue.com/images/common/bb_expand.gif) no-repeat right 50%; } #nav li { line-height: 22px; position: relative; } #nav li ul { position: absolute; left: -999em; 150px; font-weight: normal; margin: 0px; padding: 0px; } #nav li li { 150px; } #nav li ul a { 150px; 126px; padding: 0px 12px; line-height: 22px; text-align: left; } #nav li ul ul { margin: 0px 0 0 150px; } #nav li:hover ul ul,#nav li.sfhover ul ul{ left: -999em; } #nav li:hover ul, #nav li li:hover ul,#nav li.sfhover ul, #nav li li.sfhover ul{ left: auto; } #nav li:hover ul,#nav li.sfhover ul{ left: 150px; top: 0px; } #nav li:hover, #nav li.sfhover { background: #F5E3C0; } * html #nav li { float: left; height: 1%; } * html #nav li a { height: 1%; } --> </style> </head> <body> <p><a href="javascript:history.back()">Back</a></p> <ul id="nav"> <li><a href="">Home</a></li> <li><a href="/aboutme.html">About Me</a></li> <li><a class="selected" href="/tutorials.html">Tutorials</a> <ul> <li><a href="#">Sub Menu 31</a></li> <li><a class="selected" href="#">Sub Menu 32</a> <ul> <li><a href="#">Sub Menu 321</a></li> <li><a href="#">Sub Menu 322</a></li> <li><a href="#">Sub Menu 323</a></li> <li><a href="#">Sub Menu 324</a></li> </ul> </li> <li><a href="#">Sub Menu 33</a></li> <li><a href="#">Sub Menu 34</a></li> </ul> </li> <li><a class="selected" href="/gallery/gallery.html">Gallery</a> <ul> <li><a href="#">Sub Menu 41</a></li> <li><a class="selected" href="#">Sub Menu 42</a> <ul> <li><a href="#">Sub Menu 421</a></li> <li><a href="#">Sub Menu 422</a></li> <li><a href="#">Sub Menu 423</a></li> <li><a href="#">Sub Menu 424</a></li> </ul> </li> <li><a href="#">Sub Menu 43</a></li> <li><a href="#">Sub Menu 44</a></li> </ul> </li> <li><a href="#">Contact Me</a></li> </ul> </body> </html>