:first-child CSS伪类 代表了一组兄弟元素中的第一个元素。在level3实现中，被匹配的元素需要具有一个父级元素，而在level4实现中则不需要。
语法
:first-child { style properties }
element:first-child { style properties }
示例
span:first-child {
background-color: lime;
}
上面的CSS作用于下面的HTML:
<div> <span>This span is limed!</span> <span>This span is not. :(</span> </div>
就会显示出这样的效果:
This span is limed! This span is not. :(
例子2 - 使用UL
HTML Content
<ul>
<li>List 1</li>
<li>List 2</li>
<li>List 3</li>
</ul>CSS Content
li{
color:red;
}
li:first-child{
color:green;
}... 看起来像 ...
规范
| Specification | Status | Comment |
|---|---|---|
| Selectors Level 4 :first-child |
Working Draft | No change. |
| Selectors Level 3 :first-child |
Recommendation | Initial definition. |
浏览器兼容性
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Basic support | 4.0 | 3.0 (1.9) | 7 | 9.5 | 4 |
| Feature | Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|
| Basic support | 1.0 | 1.0 (1.9.1) | 7 | 10.0 | 3.1 |
IE附注
Internet Explorer 7 doesn't update the styles when elements are added dynamically. In Internet Explorer 8, if an element is inserted dynamically by clicking on a link the first-child style isn't applied until the link loses focus.