-webkit-border-before

非标准: 该特性是非标准的，请尽量不要在生产环境中使用它！

-webkit-border-before CSS 属性是一种用于简写的属性。它用于在样式表的单个位置设置各个起始边框属性值。

/* Border values */
-webkit-border-before: 1px;
-webkit-border-before: 2px dotted;
-webkit-border-before: medium dashed blue;

/* Global values */
-webkit-border-before: inherit;
-webkit-border-before: initial;
-webkit-border-before: unset;

-webkit-border-before 可以使用以下一个或多个值:

-webkit-border-before-width
-webkit-border-before-style
-webkit-border-before-color.

它根据元素的书写模式、方向以及文本方向映射到Border上. 对应到四个边框属性border-top、border-right、border-bottom或border-left ，具体取决于 writing-mode、direction、text-orientation三个属性定义的值。

这个属性和 -webkit-border-after、-webkit-border-start、-webkit-border-end三个属性用来定义元素的边界。

此属性在相关标准上的命名为 border-block-start (en-US).

初始值	as each of the properties of the shorthand: `border-width`: as each of the properties of the shorthand: `border-top-width`: `medium` `border-right-width`: `medium` `border-bottom-width`: `medium` `border-left-width`: `medium` `border-style`: as each of the properties of the shorthand: `border-top-style`: `none` `border-right-style`: `none` `border-bottom-style`: `none` `border-left-style`: `none` `color`: `canvastext`
适用元素	all elements
是否是继承属性	yes
Percentages	as each of the properties of the shorthand: `-webkit-border-before-width`: logical-width of containing block
计算值	as each of the properties of the shorthand: `border-width`: as each of the properties of the shorthand: `border-bottom-width`: the absolute length or `0` if `border-bottom-style` is `none` or `hidden` `border-left-width`: the absolute length or `0` if `border-left-style` is `none` or `hidden` `border-right-width`: the absolute length or `0` if `border-right-style` is `none` or `hidden` `border-top-width`: the absolute length or `0` if `border-top-style` is `none` or `hidden` `border-style`: as each of the properties of the shorthand: `border-bottom-style`: as specified `border-left-style`: as specified `border-right-style`: as specified `border-top-style`: as specified `color`: computed color
Animation type	discrete

语法

可选择的值

按以下顺序，一个或多个值

<'border-width'>: 参考 border-width
<'border-style'>: 参考 border-style
<'color'>: 参考 color

Formal syntax

<'border-width'> || <'border-style'> || <color>where 
<color> = <rgb()> | <rgba()> | <hsl()> | <hsla()> | <hwb()> | <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>? )
<hwb()> = hwb( [<hue> | none] [<percentage> | none] [<percentage> | none] [ / [<alpha-value> | none] ]? )
where 
<alpha-value> = <number> | <percentage>
<hue> = <number> | <angle>

示例

HTML

<div>
  <p class="exampleText">Example text</p>
</div>

CSS

div {
  background-color: yellow;
  width: 120px;
  height: 120px;
}

.exampleText {
  writing-mode: vertical-rl;
  -webkit-border-before: 5px dashed blue;
}

规范

尽管它和 border-block-start (en-US) 属性有关，但现在并不存在与任何一标准规范。

兼容性

BCD tables only load in the browser

参考

border-block-start (en-US)
The mapped physical properties: border-top, border-right, border-bottom, and border-left
writing-mode, direction, text-orientation