---
title: 类选择器
slug: Web/CSS/Class_selectors
tags:
  - CSS
  - Selectors
translation_of: Web/CSS/Class_selectors
---
<div>{{ CSSRef() }}</div>

<h2 id="Summary" name="Summary">概述</h2>

<p>在一个HTML文档中，CSS类选择器会根据元素的类属性中的内容匹配元素。类属性被定义为一个以空格分隔的列表项，在这组类名中，必须有一项与类选择器中的类名完全匹配，此条样式声明才会生效。</p>

<h2 id="Syntax" name="Syntax">语法</h2>

<pre class="syntaxbox">.类名 {<em>样式声明</em> }</pre>

<p>注意它与下面的语句等价  {{ Cssxref("Attribute_selectors", "attribute selector") }}:</p>

<pre class="syntaxbox">[class~=类名] {<em>样式声明</em> }</pre>

<h2 id="Examples" name="Examples">示例</h2>

<pre class="brush: css">span.classy {
  background-color: DodgerBlue;
}
</pre>

<p>上面的CSS作用于下面的HTML代码:</p>

<pre class="brush: html">  &lt;span class="classy"&gt;Here's a span with some text.&lt;/span&gt;
  &lt;span&gt;Here's another.&lt;/span&gt;
</pre>

<p>则会产生这样的效果:</p>

<p><span style="background-color: DodgerBlue;">Here's a span with some text.</span></p>

<p>Here's another.</p>

<h2 id="Specifications" name="Specifications">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><a class="external" href="http://www.w3.org/TR/css3-selectors/#class-html" title="http://www.w3.org/TR/css3-selectors/#class-html">CSS Selectors Level 3</a></td>
   <td>{{ Spec2('CSS3 Selectors') }}</td>
   <td> </td>
  </tr>
  <tr>
   <td><a class="external" href="http://www.w3.org/TR/CSS21/selector.html#class-html" title="http://www.w3.org/TR/CSS21/selector.html#class-html">CSS 2.1</a></td>
   <td>{{ Spec2('CSS2.1') }}</td>
   <td> </td>
  </tr>
  <tr>
   <td><a class="external" href="http://www.w3.org/TR/CSS1/#class-as-selector" title="http://www.w3.org/TR/CSS1/#class-as-selector">CSS 1</a></td>
   <td>{{ Spec2('CSS1') }}</td>
   <td> </td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</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>{{ CompatVersionUnknown() }}</td>
   <td>{{ CompatVersionUnknown() }}</td>
   <td>{{ CompatVersionUnknown() }}</td>
   <td>{{ CompatVersionUnknown() }}</td>
   <td>{{ CompatVersionUnknown() }}</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Chrome for 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>{{ CompatUnknown() }}</td>
   <td>{{ CompatUnknown() }}</td>
   <td>{{ CompatUnknown() }}</td>
   <td>{{ CompatUnknown() }}</td>
   <td>{{ CompatUnknown() }}</td>
   <td>{{ CompatUnknown() }}</td>
  </tr>
 </tbody>
</table>
</div>

<h2 id="See_also" name="See_also">See also</h2>