CSS: 指向目标下第一层或者全部层的元素 Target first level <li>s and not the nested <li>...

Have a container <div> with a class, and use the > selector. Lets say your container div's class is "myclass":

.myclass ul li {
   ...this will affect both levels of li.
}

.myclass > ul > li {
   ...this will only affect the first level.
}

.myclass > ul > li > ul > li {
   ...this will only affect the second level.
}

Note: the > selector does not work in IE6 and below when used as a CSS selector. It does work in all other browsers though, including IE7 and IE8, and when used in JQuery, it works in all browsers supported by jQuery, including IE6.

还可以参考下面的写法:

$('ul > li:not(:has(ul))');