---
title: ':optional'
slug: 'Web/CSS/:optional'
translation_of: 'Web/CSS/:optional'
---
<p>{{ CSSRef() }}</p>

<h2 id="摘要">摘要</h2>

<p><code>:optional</code> CSS <a href="/en/CSS/Pseudo-classes" title="Pseudo-classes">伪类</a> 表示任意没有{{ htmlattrxref("required","input") }}属性的 {{ HTMLElement("input") }}，{{HTMLElement("select")}} 或  {{ HTMLElement("textarea") }} 元素使用它。</p>

<pre><code>/* Selects any optional &lt;input&gt; */
input:optional {
  border: 1px dashed black;
}</code>
</pre>

<p>它允许表单容易的展示可选字段并且渲染其外观。</p>

<div class="note">
<p>注：为必填字段设置外观，请使用 {{ cssxref(":required") }}伪类。</p>
</div>

<h2 id="语法">语法</h2>

{{csssyntax}}

<h2 id="例子">例子</h2>

<p>查看{{ cssxref(":invalid") }} 示例。</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('HTML WHATWG', '#selector-optional', ':optional') }}</td>
   <td>{{ Spec2('HTML WHATWG') }}</td>
   <td>No change.</td>
  </tr>
  <tr>
   <td>{{ SpecName('HTML5 W3C', '#selector-optional', ':optional') }}</td>
   <td>{{ Spec2('HTML5 W3C') }}</td>
   <td>Defines the semantic regarding HTML and constraint validation.</td>
  </tr>
  <tr>
   <td>{{ SpecName('CSS4 Selectors', '#opt-pseudos', ':optional') }}</td>
   <td>{{ Spec2('CSS4 Selectors') }}</td>
   <td>No change.</td>
  </tr>
  <tr>
   <td>{{ SpecName('CSS3 Basic UI', '#pseudo-required-value', ':optional') }}</td>
   <td>{{ Spec2('CSS3 Basic UI') }}</td>
   <td>Defines the pseudo-class, but not the associated semantic.</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") }}</td>
   <td>10</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") }}</td>
   <td>{{ CompatNo() }}</td>
   <td>10.0</td>
   <td>5.0</td>
  </tr>
 </tbody>
</table>
</div>

<h2 id="参见">参见</h2>

<ul>
 <li>{{ cssxref(":required") }}</li>
 <li>{{ cssxref(":invalid") }}</li>
 <li>{{ cssxref(":valid") }}</li>
 <li><a href="https://developer.mozilla.org/en-US/docs/Learn/HTML/Forms/Form_validation">Form data validation</a></li>
</ul>