---
title: border-bottom-width
slug: Web/CSS/border-bottom-width
translation_of: Web/CSS/border-bottom-width
---
<div>{{CSSRef}}</div>

<div><a href="/en/CSS" title="CSS">CSS</a> 属性 <strong><code>border-bottom-width</code></strong> 设置一个元素的底部边框宽度。</div>

<pre class="brush:css no-line-numbers">/* Keyword values */
border-bottom-width: thin;
border-bottom-width: medium;
border-bottom-width: thick;

/* &lt;length&gt; values */
border-bottom-width: 10em;
border-bottom-width: 3vmax;
border-bottom-width: 6px;

/* Global keywords */
border-bottom-width: inherit;
border-bottom-width: initial;
border-bottom-width: unset;
</pre>

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

<h2 id="Syntax" name="Syntax">Syntax</h2>

<h3 id="Values">Values</h3>

<dl>
 <dt>&lt;<code>br-width&gt;</code></dt>
 <dd>定义边框宽度，取值为非负的宽度值{{cssxref("&lt;length&gt;")}}或关键字。 如果是关键字的话，其取值必须是以下之一：
 <table class="standard-table">
  <tbody>
   <tr>
    <td style="vertical-align: middle;"><code>thin</code></td>
    <td style="vertical-align: middle;">
     <div style="margin: 0.5em; width: 3em; height: 3em; border-bottom-style: solid; border-bottom-width: thin; background-color: palegreen;"> </div>
    </td>
    <td style="vertical-align: middle;">细边框</td>
   </tr>
   <tr>
    <td style="vertical-align: middle;"><code>medium</code></td>
    <td style="vertical-align: middle;">
     <div style="margin: 0.5em; width: 3em; height: 3em; border-bottom-style: solid; border-bottom-width: medium; background-color: palegreen;"> </div>
    </td>
    <td style="vertical-align: middle;">中等边框</td>
   </tr>
   <tr>
    <td style="vertical-align: middle;"><code>thick</code></td>
    <td style="vertical-align: middle;">
     <div style="margin: 0.5em; width: 3em; height: 3em; border-bottom-style: solid; border-bottom-width: thick; background-color: palegreen;"> </div>
    </td>
    <td style="vertical-align: middle;">粗边框</td>
   </tr>
  </tbody>
 </table>

 <div class="note">
 <p><strong>Note:</strong> 因为规范没有具体定义每个关键字对应的宽度值，所以实际显示效果依赖于实现。但是宽度值的取值一定遵循 <code>thin ≤ medium ≤ thick</code> 的规律且在单文档中是常数。</p>
 </div>
 </dd>
</dl>

<h3 id="Formal_syntax">Formal syntax</h3>

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

<h2 id="Example">Example</h2>

<h3 id="HTML">HTML</h3>

<pre class="brush: html">&lt;div&gt;Element 1&lt;/div&gt;
&lt;div&gt;Element 2&lt;/div&gt;</pre>

<h3 id="CSS">CSS</h3>

<pre class="brush: css">div {
  border: 1px solid red;
  margin: 1em 0;
}

div:nth-child(1) {
  border-bottom-width: thick;
}
div:nth-child(2) {
  border-bottom-width: 2em;
}</pre>

<h3 id="Result">Result</h3>

<p>{{EmbedLiveSample('Example', '100%')}}</p>

<h2 id="Specifications" name="Specifications">Specifications</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('CSS3 Backgrounds', '#the-border-width', 'border-bottom-width') }}</td>
   <td>{{ Spec2('CSS3 Backgrounds') }}</td>
   <td>No significant change.</td>
  </tr>
  <tr>
   <td>{{SpecName('CSS2.1', 'box.html#border-width-properties', 'border-bottom-width')}}</td>
   <td>{{Spec2('CSS2.1')}}</td>
   <td>No significant change.</td>
  </tr>
  <tr>
   <td>{{SpecName('CSS1', '#border-left-width', 'border-bottom-width')}}</td>
   <td>{{Spec2('CSS1')}}</td>
   <td>Initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_Compatibility" name="Browser_Compatibility">Browser compatibility</h2>



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

<h2 id="See_Also" name="See_Also">See also</h2>

<ul>
 <li>The other border-width-related CSS properties: {{ Cssxref("border-left-width") }}, {{ Cssxref("border-right-width") }}, {{ Cssxref("border-top-width") }}, and {{ Cssxref("border-width") }}.</li>
 <li>The other border-bottom-related CSS properties: {{ Cssxref("border") }}, {{ Cssxref("border-bottom") }}, {{ Cssxref("border-bottom-style") }}, and {{ Cssxref("border-bottom-color") }}.</li>
</ul>