border-bottom

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

border-bottom 简写属性把下边框的所有属性：border-bottom-color，border-bottom-style 与 border-bottom-width 设置到了一个声明中。这些属性描述了元素的下边框样式。

尝试一下

border-bottom: solid;

border-bottom: dashed red;

border-bottom: 1rem solid;

border-bottom: thick double #32a1ce;

border-bottom: 4mm ridge rgba(211, 220, 50, 0.6);

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box with a border around it.
  </div>
</section>

#example-element {
  background-color: #eee;
  color: #8b008b;
  padding: 0.75em;
  width: 80%;
  height: 100px;
}

与所有的简记属性相同， border-bottom 定义了它所有可以定义的属性，即使他们并没有被显式地定义。它把所有未被显式定义的参数都设置为了默认值，这意味着这些值将被定义为：

css
border-bottom-style: dotted;
border-bottom: thick green;

它和以下的代码是等价的：

css
border-bottom-style: dotted;
border-bottom: none thick green;

顺便一提，在 border-bottom 之前定义的 border-bottom-style 的值因此被忽略了。由于 border-bottom-style 并没有默认值，未被定义的 border-style 参数的值将被设置为 none，也就是无底边框。

语法

css
border-bottom: 1px;
border-bottom: 2px dotted;
border-bottom: medium dashed blue;

值

<br-width>

见 border-bottom-width。

<br-style>

见 border-bottom-style。

<color>

见 border-bottom-color。

形式语法

border-bottom = 
  <line-width>  ||
  <line-style>  ||
  <color>       

<line-width> = 
  <length [0,∞]>  |
  thin            |
  medium          |
  thick           

<line-style> = 
  none    |
  hidden  |
  dotted  |
  dashed  |
  solid   |
  double  |
  groove  |
  ridge   |
  inset   |
  outset

示例

html
<div>This box has a border on the bottom side.</div>
css
div {
  border-bottom: 4px dashed blue;
  background-color: gold;
  height: 100px;
  width: 100px;
  font-weight: bold;
  text-align: center;
}

规范

Specification
CSS Backgrounds and Borders Module Level 3
# border-shorthands

浏览器兼容性