files/zh-cn/web/css/_colon_only-child/index.html


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---
title: ':only-child'
slug: 'Web/CSS/:only-child'
tags:
  - CSS
  - Layout
  - Pseudo-class
  - Reference
  - Web
translation_of: 'Web/CSS/:only-child'
---
<div>{{CSSRef}}</div>

<div></div>

<p>CSS<a href="/en-US/docs/CSS/Pseudo-classes" title="Pseudo-classes">伪类</a><code>:only-child</code> 匹配没有任何兄弟元素的元素.等效的选择器还可以写成 <code>:first-child:last-child</code>或者<code>:nth-child(1):nth-last-child(1)</code>,当然,前者的权重会低一点.</p>

<pre class="brush: css no-line-numbers">/* Selects each &lt;p&gt;, but only if it is the */
/* only child of its parent */
p:only-child {
  background-color: lime;
}</pre>

<div class="note">
<p><strong>Note</strong>: 在起初定义, 被选择的元素必须拥有一个父级元素. 从 Selectors Level 4 开始, 这不再是必须的了.</p>
</div>

<h2 id="语法">语法</h2>

{{csssyntax}}

<h2 id="示例">示例</h2>

<h3 id="基础示例">基础示例</h3>

<h4 id="HTML">HTML</h4>

<pre class="brush: html">&lt;main&gt;
  &lt;div&gt;
    &lt;i&gt;I am a lonely only child.&lt;/i&gt;
  &lt;/div&gt;

  &lt;div&gt;
    &lt;i&gt;I have siblings.&lt;/i&gt;&lt;br&gt;
    &lt;b&gt;So do I!&lt;/b&gt;&lt;br&gt;
    &lt;span&gt;I also have siblings, &lt;span&gt;but this is an only child.&lt;/span&gt;&lt;/span&gt;
  &lt;/div&gt;
&lt;/main&gt;</pre>

<h4 id="CSS">CSS</h4>

<pre class="brush: css">main :only-child {
  color: red;
}
</pre>

<h4 id="结果">结果</h4>

<p>{{EmbedLiveSample('基础示例','100%',180)}}</p>

<h3 id="一个列表示例">一个列表示例</h3>

<h4 id="HTML_2">HTML</h4>

<pre class="brush: html">&lt;ol&gt;
  &lt;li&gt;First
    &lt;ul&gt;
      &lt;li&gt;This list has just one element.&lt;/li&gt;
    &lt;/ul&gt;
  &lt;/li&gt;
  &lt;li&gt;Second
    &lt;ul&gt;
      &lt;li&gt;This list has three elements.&lt;/li&gt;
      &lt;li&gt;This list has three elements.&lt;/li&gt;
      &lt;li&gt;This list has three elements.&lt;/li&gt;
    &lt;/ul&gt;
  &lt;/li&gt;
&lt;/ol&gt;
</pre>

<h4 id="CSS_2">CSS</h4>

<pre class="brush: css">li li {
  list-style-type: disc;
}
li:only-child {
  color: red;
  list-style-type: square;
}</pre>

<h4 id="结果_2">结果</h4>

<p>{{EmbedLiveSample('一个列表示例', '100%', 210)}}</p>

<h2 id="规范">规范</h2>

<table class="standard-table">
 <thead>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
 </thead>
 <tbody>
  <tr>
   <td>{{SpecName('CSS4 Selectors', '#only-child-pseudo', ':only-child')}}</td>
   <td>{{Spec2('CSS4 Selectors')}}</td>
   <td>Matching elements are not required to have a parent.</td>
  </tr>
  <tr>
   <td>{{SpecName('CSS3 Selectors', '#only-child-pseudo', ':only-child')}}</td>
   <td>{{Spec2('CSS3 Selectors')}}</td>
   <td>Initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

<div>
<div>


<p>{{Compat("css.selectors.only-child")}}</p>
</div>
</div>

<h2 id="另见">另见</h2>

<ul>
 <li>{{Cssxref(":only-of-type")}}</li>
 <li>{{Cssxref(":first-child")}}</li>
 <li>{{Cssxref(":last-child")}}</li>
 <li>{{Cssxref(":nth-child")}}</li>
</ul>