border-bottom

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。

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 https://github.com/mdn/interactive-examples and send us a pull request.

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：

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

它和以下的代码是等价的：

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。

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

<br-width>

见 border-bottom-width。

<br-style>

见 border-bottom-style。

<color>

见 border-bottom-color。

<line-width> || <line-style> || <color>
where 
<line-width> = <length> | thin | medium | thick
<line-style> = none | hidden | dotted | dashed | solid | double | groove | ridge | inset | outset
<color> = <rgb()> | <rgba()> | <hsl()> | <hsla()> | <hex-color> | <named-color> | currentcolor | <deprecated-system-color>
where 
<rgb()> = rgb( <percentage>{3} [ / <alpha-value> ]? ) | rgb( <number>{3} [ / <alpha-value> ]? ) | rgb( <percentage>#{3} , <alpha-value>? ) | rgb( <number>#{3} , <alpha-value>? )
<rgba()> = rgba( <percentage>{3} [ / <alpha-value> ]? ) | rgba( <number>{3} [ / <alpha-value> ]? ) | rgba( <percentage>#{3} , <alpha-value>? ) | rgba( <number>#{3} , <alpha-value>? )
<hsl()> = hsl( <hue> <percentage> <percentage> [ / <alpha-value> ]? ) | hsl( <hue>, <percentage>, <percentage>, <alpha-value>? )
<hsla()> = hsla( <hue> <percentage> <percentage> [ / <alpha-value> ]? ) | hsla( <hue>, <percentage>, <percentage>, <alpha-value>? )
where 
<alpha-value> = <number> | <percentage>
<hue> = <number> | <angle>

<div>
  This box has a border on the bottom side.
</div>

div {
  border-bottom: 4px dashed blue;
  background-color: gold;
  height: 100px;
  width: 100px;
  font-weight: bold;
  text-align: center;
}