---
title: border-left
slug: Web/CSS/border-left
tags:
  - CSS
  - CSS 属性
  - CSS 边框
translation_of: Web/CSS/border-left
---
<div>{{CSSRef}}</div>

<p>CSS属性 <strong>border-left</strong> 是属性{{ Cssxref("border-left-color") }}, {{ Cssxref("border-left-style") }}, 和{{ Cssxref("border-left-width") }}的三者的缩写。这些属性都是在描述一个元素的左边的边框{{cssxref("border")}}。</p>

<pre class="brush:css no-line-numbers">border-left: 1px;
border-left: 2px dotted;
border-left: medium dashed green;
</pre>

<p>这三种属性值的缩写需要按照顺序定义数值，也可以省略其中的一个或者两个。</p>

<div class="note">
<p>和CSS所有的缩写属性一样，border-left 总是会设置该缩写属性所包含的全部属性值，即使开发者并没有一一指定这些值。CSS缩写属性会给没有被定义的属性一个默认的属性值。那就意味着下面这个例子......</p>

<pre class="brush: css">border-left-style: dotted;
border-left: thick green;
</pre>

<p>......实际上应该是下面这个样子......</p>

<pre class="brush: css">border-left-style: dotted;
border-left: none thick green;
</pre>

<p>......并且在 border-left 之前定义的 {{ Cssxref("border-left-style") }} 的值也会被覆盖。由于 {{ Cssxref("border-left-style") }} 的默认值是 none, border-style的最终结果就是没有边框。</p>
</div>

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

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

<p>这三种属性值的缩写需要按照顺序定义数值，也可以省略其中的一个或者两个。</p>

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

<dl>
 <dt><code>&lt;br-width&gt; </code></dt>
 <dd>请参阅{{ Cssxref("border-left-width") }}.</dd>
 <dt><code>&lt;br-style&gt; </code></dt>
 <dd>请参阅{{ Cssxref("border-left-style") }}.</dd>
 <dt><code>{{cssxref("&lt;color&gt;")}}</code></dt>
 <dd>请参阅 {{ Cssxref("border-left-color") }}.</dd>
</dl>

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

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

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

<pre class="brush: html">&lt;div&gt;
  This box has a border on the left side.
&lt;/div&gt;</pre>

<pre class="brush: css">div {
  border-left: 4px dashed blue;
  background-color: gold;
  height: 100px;
  width: 100px;
  font-weight: bold;
  text-align: center;
}
</pre>

<p>{{ EmbedLiveSample('Example') }}</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', '#border-left', 'border-left') }}</td>
   <td>{{ Spec2('CSS3 Backgrounds') }}</td>
   <td>No direct changes, though the modification of values for the {{ cssxref("border-left-color") }} do apply to it.</td>
  </tr>
  <tr>
   <td>{{ SpecName('CSS2.1', 'box.html#propdef-border-left', 'border-left') }}</td>
   <td>{{ Spec2('CSS2.1') }}</td>
   <td>No significant changes.</td>
  </tr>
  <tr>
   <td>{{ SpecName('CSS1', '#border-left', 'border-left') }}</td>
   <td>{{ Spec2('CSS1') }}</td>
   <td>Initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility" name="Browser_compatibility">Browser compatibility</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 (WebKit)</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>1.0</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{ CompatGeckoDesktop("1.0") }}</td>
   <td>4</td>
   <td>3.5</td>
   <td>1.0 (85)</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 Phone</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>1.0</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{ CompatGeckoMobile("1.0") }}</td>
   <td>{{ CompatVersionUnknown() }}</td>
   <td>{{ CompatVersionUnknown() }}</td>
   <td>{{ CompatVersionUnknown() }}</td>
  </tr>
 </tbody>
</table>
</div>