border-bottom

尝试一下

border-bottom 简写属性把下边框的所有属性:border-bottom-colorborder-bottom-styleborder-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。

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。

语法

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

<br-width>
border-bottom-width
<br-style>
border-bottom-style
<color>
border-bottom-color

形式化语法

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

<color> =
<absolute-color-base> |
currentcolor |
<system-color> |
<device-cmyk()>

<absolute-color-base> =
<hex-color> (en-US) |
<named-color> |
transparent |
<rgb()> |
<rgba()> |
<hsl()> |
<hsla()> |
<hwb()> |
<lab()> |
<lch()> |
<oklab()> |
<oklch()> |
<color()>

<device-cmyk()> =
device-cmyk( <cmyk-component>{4} [ / <alpha-value> ]? )

<rgb()> =
rgb( [ <percentage> | none ]{3} [ / [ <alpha-value> | none ] ]? ) |
rgb( [ <number> | none ]{3} [ / [ <alpha-value> | none ] ]? )

<hsl()> =
hsl( [ <hue> | none ] [ <percentage> | none ] [ <percentage> | none ] [ / [ <alpha-value> | none ] ]? )

<hwb()> =
hwb( [ <hue> | none ] [ <percentage> | none ] [ <percentage> | none ] [ / [ <alpha-value> | none ] ]? )

<lab()> =
lab( [ <percentage> | <number> | none ] [ <percentage> | <number> | none ] [ <percentage> | <number> | none ] [ / [ <alpha-value> | none ] ]? )

<lch()> =
lch( [ <percentage> | <number> | none ] [ <percentage> | <number> | none ] [ <hue> | none ] [ / [ <alpha-value> | none ] ]? )

<oklab()> =
oklab( [ <percentage> | <number> | none ] [ <percentage> | <number> | none ] [ <percentage> | <number> | none ] [ / [ <alpha-value> | none ] ]? )

<oklch()> =
oklch( [ <percentage> | <number> | none ] [ <percentage> | <number> | none ] [ <hue> | none ] [ / [ <alpha-value> | none ] ]? )

<color()> =
color( <colorspace-params> [ / [ <alpha-value> | none ] ]? )

<cmyk-component> =
<number> |
<percentage>

<alpha-value> =
<number> |
<percentage>

<hue> =
<number> |
<angle> |
none

<colorspace-params> =
<predefined-rgb-params> |
<xyz-params>

<predefined-rgb-params> =
<predefined-rgb> [ <number> | <percentage> | none ]{3}

<xyz-params> =
<xyz-space> [ <number> | none ]{3}

<predefined-rgb> =
srgb |
srgb-linear |
display-p3 |
a98-rgb |
prophoto-rgb |
rec2020

<xyz-space> =
xyz |
xyz-d50 |
xyz-d65

示例

<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;
}

规则

规则 状态 评价
CSS Backgrounds and Borders Module Level 3
border-bottom
Candidate Recommendation 没有直接的改变,即使 border-bottom-color 值的修改被确定。
CSS Level 2 (Revision 1)
border-bottom
Recommendation 没有显著的变化。
CSS Level 1
border-bottom
Recommendation 初始定义。

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