---
title: ':default'
slug: 'Web/CSS/:default'
translation_of: 'Web/CSS/:default'
---
<div>{{CSSRef}}</div>

<p> <strong><code>:default</code></strong> <a href="https://developer.mozilla.org/en-US/docs/Web/CSS">CSS</a> <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/Pseudo-classes">pseudo-class</a> 表示一组相关元素中的默认表单元素。</p>

<p>该选择器可以在 {{htmlelement("button")}}, <code><a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/checkbox">&lt;input type="checkbox"&gt;</a></code>, <code><a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/radio">&lt;input type="radio"&gt;</a></code>, 以及 {{htmlelement("option")}} 上使用。</p>

<pre class="brush: css no-line-numbers  language-css"><code class="language-css"><span class="comment token">/* Selects any default &lt;input&gt; */</span>
<span class="selector token">input<span class="pseudo-class token">:default</span> </span><span class="punctuation token">{</span>
  <span class="property token">background-color</span><span class="punctuation token">:</span> lime<span class="punctuation token">;</span>
<span class="punctuation token">}</span></code></pre>

<p>允许多个选择的分组元素也可以具有多个默认值，即，它们可以具有最初选择的多个项目。在这种情况下，所有默认值都使用 <code>:default</code> 伪类表示。例如，您可以在一组复选框之间设置默认复选框。</p>

<h2 id="语法">语法</h2>

{{csssyntax}}

<h2 id="示例">示例</h2>

<h3 id="HTML">HTML</h3>

<pre class="brush: html">&lt;input type="radio" name="season" id="spring"&gt;
&lt;label for="spring"&gt;Spring&lt;/label&gt;

&lt;input type="radio" name="season" id="summer" checked&gt;
&lt;label for="summer"&gt;Summer&lt;/label&gt;

&lt;input type="radio" name="season" id="fall"&gt;
&lt;label for="fall"&gt;Fall&lt;/label&gt;

&lt;input type="radio" name="season" id="winter"&gt;
&lt;label for="winter"&gt;Winter&lt;/label&gt;</pre>

<h3 id="CSS">CSS</h3>

<pre class="brush: css">input:default {
  box-shadow: 0 0 2px 1px coral;
}

input:default + label {
  color: coral;
}</pre>

<h3 id="结果">结果</h3>

<p>{{EmbedLiveSample('示例')}}</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">说明</th>
  </tr>
 </thead>
 <tbody>
  <tr>
   <td>{{SpecName('HTML WHATWG', '#selector-default', ':default')}}</td>
   <td>{{Spec2('HTML WHATWG')}}</td>
   <td>无变化</td>
  </tr>
  <tr>
   <td>{{SpecName('HTML5 W3C', '#selector-default', ':default')}}</td>
   <td>{{Spec2('HTML5 W3C')}}</td>
   <td>定义了HTML语义和规范验证</td>
  </tr>
  <tr>
   <td>{{SpecName('CSS4 Selectors', '#default-pseudo', ':default')}}</td>
   <td>{{Spec2('CSS4 Selectors')}}</td>
   <td>无变化</td>
  </tr>
  <tr>
   <td>{{SpecName('CSS3 Basic UI', '#pseudo-default', ':default')}}</td>
   <td>{{Spec2('CSS3 Basic UI')}}</td>
   <td>定义了伪类，但不关联伪类</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>10.0</td>
   <td>{{CompatGeckoDesktop("2.0")}}</td>
   <td>{{CompatNo}}</td>
   <td>10.0</td>
   <td>5.0</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>{{CompatUnknown}}</td>
   <td>{{CompatGeckoMobile("2.0")}}</td>
   <td>{{CompatNo}}</td>
   <td>10.0</td>
   <td>5.0</td>
  </tr>
 </tbody>
</table>
</div>