border-left

CSS属性 border-left 是属性border-left-color, border-left-style, 和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border。

border-left: 1px;
border-left: 2px dotted;
border-left: medium dashed green;

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。

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......

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

......实际上应该是下面这个样子......

border-left-style: dotted;
border-left: none thick green;

......并且在 border-left 之前定义的 border-left-style 的值也会被覆盖。由于 border-left-style 的默认值是 none, border-style的最终结果就是没有边框。

初始值	as each of the properties of the shorthand: `border-left-width`: `medium` `border-left-style`: `none` `border-left-color`: `currentcolor`
适用元素	all elements. It also applies to `::first-letter`.
是否是继承属性	否
计算值	as each of the properties of the shorthand: `border-left-width`: the absolute length or `0` if `border-left-style` is `none` or `hidden` `border-left-style`: as specified `border-left-color`: computed color
Animation type	as each of the properties of the shorthand: `border-left-color`: a color `border-left-style`: discrete `border-left-width`: a length

Syntax

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。

Values

<br-width>: 请参阅border-left-width.
<br-style>: 请参阅border-left-style.
<color>: 请参阅 border-left-color.

Formal syntax

<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>

Example

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

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

Specifications

Specification	Status	Comment
CSS Backgrounds and Borders Module Level 3 border-left	Candidate Recommendation	No direct changes, though the modification of values for the `border-left-color` do apply to it.
CSS Level 2 (Revision 1) border-left	Recommendation	No significant changes.
CSS Level 1 border-left	Recommendation	Initial definition.

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help! (en-US)

Desktop
Mobile

Feature	Chrome	Edge	Firefox (Gecko)	Internet Explorer	Opera	Safari (WebKit)
Basic support	1.0	(Yes)	1.0 (1.7 or earlier)	4	3.5	1.0 (85)

Feature	Android	Edge	Firefox Mobile (Gecko)	IE Phone	Opera Mobile	Safari Mobile
Basic support	1.0	(Yes)	1.0 (1.0)	(Yes)	(Yes)	(Yes)