CSS标识当前位置页效果的实现原理

<ul id=\"nav\">
<li id=\"m1\"><a href=\"index.html\">Home</a></li>
<li id=\"m2\"><a href=\"about.html\">About</a></li>
<li id=\"m3\"><a href=\"products.html\">Products</a></li>
<li id=\"m4\"><a href=\"services.html\">Services</a></li>
<li id=\"m5\"><a href=\"contact.html\">Contact</a></li>
</ul>

#home
#nav li#m1 a,
#about #nav li#m2 a,
#products #nav li#m3 a,
#services #nav li#m4 a,
#contact #nav li#m5 a{
color: #FFF;
background: #DC4E1B url(navbg.gif) no-repeat;
}