---
title: ':root'
slug: 'Web/CSS/:root'
tags:
  - CSS
  - CSS 伪类
translation_of: 'Web/CSS/:root'
---
<div>{{CSSRef}}</div>

<h2 id="概述">概述</h2>

<p><strong><code>:root</code></strong> 这个 CSS <a href="/zh-CN/docs/Web/CSS/Pseudo-classes">伪类</a>匹配文档树的根元素。对于 HTML 来说，<strong><code>:root</code></strong> 表示 {{HTMLElement("html")}} 元素，除了<a href="/zh-CN/docs/Web/CSS/Specificity">优先级</a>更高之外，与 <code>html</code> 选择器相同。</p>

<h2 id="语法">语法</h2>

<pre class="syntaxbox">{{csssyntax}}</pre>

<h2 id="示例">示例</h2>

<p>在声明全局 <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/--*">CSS 变量</a>时 <strong><code>:root</code></strong> 会很有用：</p>

<pre class="brush: css">:root {
  --main-color: hotpink;
  --pane-padding: 5px 42px;
}
</pre>

<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('CSS4 Selectors', '#root-pseudo', ':root')}}</td>
   <td>{{Spec2('CSS4 Selectors')}}</td>
   <td>No change</td>
  </tr>
  <tr>
   <td>{{SpecName('CSS3 Selectors', '#root-pseudo', ':root')}}</td>
   <td>{{Spec2('CSS3 Selectors')}}</td>
   <td>Initial definition</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>Edge</th>
   <th>Firefox (Gecko)</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>1</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatGeckoDesktop("1.7")}}</td>
   <td>9</td>
   <td>9.5</td>
   <td>1.0</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Edge</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>{{CompatVersionUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>