---
title: ':nth-child'
slug: 'Web/CSS/:nth-child'
tags:
- ':nth-child'
- CSS
- CSS 伪类
translation_of: 'Web/CSS/:nth-child'
---
<div>{{CSSRef}}</div>
<h2 id="Summary" name="Summary">概述</h2>
<p><strong><code>:nth-child(an+b)</code></strong> 这个 <a href="/en-US/docs/CSS/Pseudo-classes">CSS 伪类</a>首先找到所有当前元素的兄弟元素，然后按照位置先后顺序从1开始排序，选择的结果为CSS伪类:nth-child括号中表达式（an+b）匹配到的元素集合（n=0，1，2，3...）。示例：</p>
<ul>
<li><code>0n+3</code> 或简单的 <code>3</code> 匹配第三个元素。</li>
<li><code>1n+0</code> 或简单的 <code>n</code> 匹配每个元素。（兼容性提醒：在 Android 浏览器 4.3 以下的版本 <code>n</code> 和 <code>1n</code> 的匹配方式不一致。<code>1n</code> 和 <code>1n+0</code> 是一致的，可根据喜好任选其一来使用。）</li>
<li><code>2n+0</code> 或简单的 <code>2n</code> 匹配位置为 2、4、6、8...的元素（n=0时，2n+0=0，第0个元素不存在，因为是从1开始排序)。你可以使用关键字 <strong><code>even</code></strong> 来替换此表达式。</li>
<li><code>2n+1</code> 匹配位置为 1、3、5、7...的元素。你可以使用关键字 <strong><code>odd</code></strong> 来替换此表达式。</li>
<li><code>3n+4</code> 匹配位置为 4、7、10、13...的元素。</li>
</ul>
<p><code><em>a</em></code> 和 <code><em>b</em></code> 都必须为整数，并且元素的第一个子元素的下标为 1。换言之就是，该伪类匹配所有下标在集合 { an + b; n = 0, 1, 2, ...} 中的子元素。另外需要特别注意的是，<code><em>an</em></code> 必须写在 <code><em>b</em></code> 的前面，不能写成 <code><em>b+an</em></code> 的形式。</p>
<h2 id="Syntax" name="Syntax">语法</h2>
{{csssyntax}}
<h2 id="示例">示例</h2>
<h3 id="选择器示例">选择器示例</h3>
<dl>
<dt><code>tr:nth-child(2n+1)</code></dt>
<dd>表示HTML表格中的奇数行。</dd>
<dt><code>tr:nth-child(odd)</code></dt>
<dd>表示HTML表格中的奇数行。</dd>
<dt><code>tr:nth-child(2n)</code></dt>
<dd>表示HTML表格中的偶数行。</dd>
<dt><code>tr:nth-child(even)</code></dt>
<dd>表示HTML表格中的偶数行。</dd>
<dt><code>span:nth-child(0n+1)</code></dt>
<dd>表示子元素中第一个且为span的元素，与 <span style="background-color: #ffffff; color: #4d4e53; font-family: open sans,arial,sans-serif; font-size: 14px; line-height: 21px;">{{Cssxref(":first-child")}} </span>选择器作用相同。</dd>
<dt><code>span:nth-child(1)</code></dt>
<dd>表示父元素中子元素为第一的并且名字为span的标签被选中</dd>
<dt><code>span:nth-child(-n+3)</code></dt>
<dd>匹配前三个子元素中的span元素。</dd>
</dl>
<h3 id="Detailed_example">Detailed example</h3>
<h4 id="HTML">HTML</h4>
<pre class="brush:html"><h3><code>span:nth-child(2n+1)</code>, WITHOUT an
<code>&lt;em&gt;</code> among the child elements.</h3>
<p>Children 1, 3, 5, and 7 are selected.</p>
<div class="first">
<span>Span 1!</span>
<span>Span 2</span>
<span>Span 3!</span>
<span>Span 4</span>
<span>Span 5!</span>
<span>Span 6</span>
<span>Span 7!</span>
</div>
<br>
<h3><code>span:nth-child(2n+1)</code>, WITH an
<code>&lt;em&gt;</code> among the child elements.</h3>
<p>Children 1, 5, and 7 are selected.<br>
3 is used in the counting because it is a child, but it isn't
selected because it isn't a <code>&lt;span&gt;</code>.</p>
<div class="second">
<span>Span!</span>
<span>Span</span>
<em>This is an `em`.</em>
<span>Span</span>
<span>Span!</span>
<span>Span</span>
<span>Span!</span>
<span>Span</span>
</div>
<br>
<h3><code>span:nth-of-type(2n+1)</code>, WITH an
<code>&lt;em&gt;</code> among the child elements.</h3>
<p>Children 1, 4, 6, and 8 are selected.<br>
3 isn't used in the counting or selected because it is an <code>&lt;em&gt;</code>,
not a <code>&lt;span&gt;</code>, and <code>nth-of-type</code> only selects
children of that type. The <code>&lt;em&gt;</code> is completely skipped
over and ignored.</p>
<div class="third">
<span>Span!</span>
<span>Span</span>
<em>This is an `em`.</em>
<span>Span!</span>
<span>Span</span>
<span>Span!</span>
<span>Span</span>
<span>Span!</span>
</div>
</pre>
<h4 id="CSS">CSS</h4>
<pre class="brush: css">html {
font-family: sans-serif;
}
span,
div em {
padding: 5px;
border: 1px solid green;
display: inline-block;
margin-bottom: 3px;
}
.first span:nth-child(2n+1),
.second span:nth-child(2n+1),
.third span:nth-of-type(2n+1) {
background-color: lime;
}</pre>
<h4 id="最终效果：">最终效果：</h4>
<p>{{EmbedLiveSample('Detailed_example', 550, 550)}}</p>
<h2 id="规范">规范</h2>
<table class="standard-table">
<thead>
<tr>
<th scope="col">规范</th>
<th scope="col">状态</th>
<th scope="col">备注</th>
</tr>
</thead>
<tbody>
<tr>
<td>{{SpecName('CSS4 Selectors', '#nth-child-pseudo', ':nth-child')}}</td>
<td>{{Spec2('CSS4 Selectors')}}</td>
<td>未变化。</td>
</tr>
<tr>
<td>{{SpecName('CSS3 Selectors', '#nth-child-pseudo', ':nth-child')}}</td>
<td>{{Spec2('CSS3 Selectors')}}</td>
<td>初始化定义。</td>
</tr>
</tbody>
</table>
<h2 id="兼容性">兼容性</h2>
<p>{{CompatibilityTable}}</p>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Chrome</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
</tr>
<tr>
<td>Basic support</td>
<td>1.0</td>
<td>{{CompatGeckoDesktop("1.9.1")}}</td>
<td>9.0</td>
<td>9.5</td>
<td>3.1<span style="font-size: 14px; line-height: 1.5;"> </span></td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Android</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Mobile</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
</tr>
<tr>
<td>Basic support</td>
<td>2.1</td>
<td>{{CompatGeckoMobile("1.9.1")}}</td>
<td>9.0</td>
<td>9.5</td>
<td>3.1</td>
</tr>
</tbody>
</table>
</div>
<h2 id="注意">注意</h2>
<ul>
<li>Opera 不能处理动态插入的元素。</li>
</ul>
<h2 id="参见">参见</h2>
<ul>
<li>{{ Cssxref(":nth-of-type") }}, {{ Cssxref(":nth-last-child") }}</li>
</ul>