---
title: width
slug: Web/CSS/width
tags:
  - CSS
  - 参考
  - 大小
  - 宽度
translation_of: Web/CSS/width
---
<div>{{CSSRef}}</div>

<p><strong><code>width</code></strong> 属性用于设置元素的宽度。<code>width</code> 默认设置<a href="/en-US/docs/CSS/CSS_Box_Model/Introduction_to_the_CSS_box_model#content-area">内容区域</a>的宽度，但如果 {{cssxref("box-sizing")}} 属性被设置为 <code>border-box</code>，就转而设置<a href="/en-US/docs/Web/CSS/CSS_Box_Model/Introduction_to_the_CSS_box_model#border-area">边框区域</a>的宽度。</p>

<div>{{EmbedInteractiveExample("pages/css/width.html")}}</div>

<p class="hidden">The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone <a href="https://github.com/mdn/interactive-examples">https://github.com/mdn/interactive-examples</a> and send us a pull request.</p>

<p>{{ cssxref("min-width") }} 和 {{ cssxref("max-width") }} 属性的优先级高于 {{ cssxref("width") }}。</p>

<h2 id="语法">语法</h2>

<pre class="brush:css no-line-numbers">/* &lt;length&gt; values */
width: 300px;
width: 25em;

/* &lt;percentage&gt; value */
width: 75%;

/* Keyword values */
width: max-content;
width: min-content;
width: fit-content(20em);
width: auto;

/* Global values */
width: inherit;
width: initial;
width: unset;
</pre>

<p><code>width</code> 属性也指定为：</p>

<ul>
 <li>下面关键字值之一：<code><a href="https://wiki.developer.mozilla.org/zh-CN/docs/Web/CSS/width$edit#min-content">min-content</a></code>，<code><a href="https://wiki.developer.mozilla.org/zh-CN/docs/Web/CSS/width$edit#max-content">max-content</a></code>，<code><a href="https://wiki.developer.mozilla.org/zh-CN/docs/Web/CSS/width$edit#fit-content">fit-content</a></code>，<code><a href="https://wiki.developer.mozilla.org/zh-CN/docs/Web/CSS/width$edit#auto">auto</a></code>。</li>
 <li>一个长度值 <code><a href="https://wiki.developer.mozilla.org/zh-CN/docs/Web/CSS/width$edit#%3Clength%3E">&lt;length&gt;</a></code> 或者百分比值 <code><a href="https://wiki.developer.mozilla.org/zh-CN/docs/Web/CSS/width$edit#%3Cpercentage%3E">&lt;percentage&gt;</a></code>。</li>
</ul>

<h3 id="值">值</h3>

<dl>
 <dt>{{cssxref("&lt;length&gt;")}}</dt>
 <dd>使用绝对值定义宽度。</dd>
 <dt>{{cssxref("&lt;percentage&gt;")}}</dt>
 <dd>使用外层元素的容纳区块宽度（the containing block's width）的百分比定义宽度。</dd>
 <dt><code>auto</code></dt>
 <dd>浏览器将会为指定的元素计算并选择一个宽度。</dd>
 <dt><code>max-content</code> {{ experimental_inline }}</dt>
 <dd>元素内容固有的（intrinsic）合适宽度。</dd>
 <dt><code>min-content</code> {{ experimental_inline }}</dt>
 <dd>元素内容固有的最小宽度。</dd>
 <dt><code>fit-content</code> {{ experimental_inline }}</dt>
 <dd>取以下两种值中的较大值:
 <ul>
  <li>固有的最小宽度</li>
  <li>固有首选宽度（max-content）和可用宽度（available）两者中的较小值</li>
 </ul>
 可表示为：<code>min(max-content, max(min-content, &lt;length-percentage&gt;))</code></dd>
</dl>

<h3 id="形式化语法">形式化语法</h3>

{{csssyntax}}

<h2 id="示例">示例</h2>

<h3 id="默认宽度">默认宽度</h3>

<pre class="brush:css">p.goldie {
  background: gold;
}</pre>

<pre class="brush:html">&lt;p class="goldie"&gt;The Mozilla community produces a lot of great software.&lt;/p&gt;</pre>

<p>{{EmbedLiveSample('Default_width', '500px', '64px')}}</p>

<h3 id="像素_px_和字高_em">像素 px 和字高 em</h3>

<pre class="brush: css">.px_length {
  width: 200px;
  background-color: red;
  color: white;
  border: 1px solid black;
}

.em_length {
  width: 20em;
  background-color: white;
  color: red;
  border: 1px solid black;
}
</pre>

<pre class="brush: html">&lt;div class="px_length"&gt;以 px 度量的宽度&lt;/div&gt;
&lt;div class="em_length"&gt;以 em 度量的宽度&lt;/div&gt;</pre>

<p>{{EmbedLiveSample('Pixels_and_ems', '500px', '64px')}}</p>

<h3 id="百分比">百分比</h3>

<pre class="brush: css">.percent {
  width: 20%;
  background-color: silver;
  border: 1px solid red;
}</pre>

<pre class="brush: html">&lt;div class="percent"&gt;按照百分比度量的宽度&lt;/div&gt;</pre>

<p>{{EmbedLiveSample('百分比', '500px', '64px')}}</p>

<h3 id="max-content"><code>max-content</code></h3>

<pre class="brush:css;">p.maxgreen {
  background: lightgreen;
  width: intrinsic;           /* Safari/WebKit 使用了非标准的名称 */
  width: -moz-max-content;    /* Firefox/Gecko */
  width: -webkit-max-content; /* Chrome */
}</pre>

<pre class="brush:html">&lt;p class="maxgreen"&gt;The Mozilla community produces a lot of great software.&lt;/p&gt;</pre>

<p>{{EmbedLiveSample('max-content', '500px', '64px')}}</p>

<h3 id="min-content"><code>min-content</code></h3>

<pre class="brush:css">p.minblue {
  background: lightblue;
  width: -moz-min-content;    /* Firefox */
  width: -webkit-min-content; /* Chrome */
}</pre>

<pre class="brush:html">&lt;p class="minblue"&gt;The Mozilla community produces a lot of great software.&lt;/p&gt;</pre>

<p>{{EmbedLiveSample('min-content', '500px', '155px')}}</p>

<h2 id="无障碍考虑">无障碍考虑</h2>

<p>当页面放大以增加文本大小时，请确保 <code>width</code> 设置的元素不会被截断并且不会遮挡其他内容。</p>

<ul>
 <li><a href="https://wiki.developer.mozilla.org/en-US/docs/Web/Accessibility/Understanding_WCAG/Perceivable#Guideline_1.4_Make_it_easier_for_users_to_see_and_hear_content_including_separating_foreground_from_background">MDN Understanding WCAG, Guideline 1.4 explanations</a></li>
 <li><a href="https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-scale.html" rel="noopener">Understanding Success Criterion 1.4.4  | Understanding WCAG 2.0</a></li>
</ul>

<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">注释</th>
  </tr>
 </thead>
 <tbody>
  <tr>
   <td>{{ SpecName('CSS3 Box', '#the-width-and-height-properties', 'width') }}</td>
   <td>{{Spec2('CSS3 Box')}}</td>
   <td>增加 <code>max-content</code>, <code>min-content</code>, <code>available</code>, <code>fit-content</code>, <code>border-box</code>, <code>content-box</code> 关键字。</td>
  </tr>
  <tr>
   <td>{{ SpecName('CSS2.1', 'visudet.html#the-width-property', 'width') }}</td>
   <td>{{Spec2('CSS2.1')}}</td>
   <td>明确了此属性对哪些元素有效。</td>
  </tr>
  <tr>
   <td>{{ SpecName('CSS1', '#width', 'width') }}</td>
   <td>{{Spec2('CSS1')}}</td>
   <td>初始定义。</td>
  </tr>
 </tbody>
</table>

<p>{{cssinfo}}</p>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

<p>{{Compat("css.properties.width")}}</p>

<div class="hidden">
<p>The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</p>
</div>

<h2 id="另请参见">另请参见</h2>

<ul>
 <li><a href="/zh-CN/docs/Web/CSS/CSS_Box_Model/Introduction_to_the_CSS_box_model">框盒模型</a></li>
 <li>{{cssxref("height")}}</li>
 <li>{{cssxref("box-sizing")}}</li>
 <li>{{cssxref("min-width")}}</li>
 <li>{{cssxref("max-width")}}</li>
</ul>