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

<h2 id="摘要">摘要</h2>

<p><code>:required</code>  <a href="/zh-CN/docs/Web/CSS">CSS</a> <a href="/en/CSS/Pseudo-classes" title="Pseudo-classes">伪类</a> 表示任意设置了{{ htmlattrxref("required", "input") }}属性的{{ HTMLElement("input") }}，{{HTMLElement("select")}}, 或 {{HTMLElement("textarea")}}元素。 这个伪类对于高亮显示在提交表单之前必须具有有效数据的字段非常有用。</p>

<p>注意：{{ cssxref(":optional") }}伪类选中'可选的'表单字段。</p>

<h2 id="语法">语法</h2>

{{csssyntax}}

<h2 id="例子">例子</h2>

<p>查看示例 {{ cssxref(":invalid") }} .</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-required', ':required') }}</td>
   <td>{{ Spec2('HTML WHATWG') }}</td>
   <td>No change.</td>
  </tr>
  <tr>
   <td>{{ SpecName('HTML5 W3C', '#selector-required', ':required') }}</td>
   <td>{{ Spec2('HTML5 W3C') }}</td>
   <td>Defines the semantic regarding HTML and constraint validation.</td>
  </tr>
  <tr>
   <td>{{ SpecName('CSS4 Selectors', '#opt-pseudos', ':required') }}</td>
   <td>{{ Spec2('CSS4 Selectors') }}</td>
   <td>No change.</td>
  </tr>
  <tr>
   <td>{{ SpecName('CSS3 Basic UI', '#pseudo-required-value', ':required') }}</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">浏览器兼容</h2>

{{Compat("css.selectors.required")}}

<h2 id="参见">参见</h2>

<ul>
 <li>{{ cssxref(":optional") }}, {{ cssxref(":invalid") }}, {{ cssxref(":valid") }}</li>
</ul>