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---
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 <input> */
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>
{{Compat("css.selectors.optional")}}
<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>
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