border-bottom-width - CSS（层叠样式表） 编辑

CSS 属性 border-bottom-width 设置一个元素的底部边框宽度。

/* Keyword values */
border-bottom-width: thin;
border-bottom-width: medium;
border-bottom-width: thick;

/* <length> values */
border-bottom-width: 10em;
border-bottom-width: 3vmax;
border-bottom-width: 6px;

/* Global keywords */
border-bottom-width: inherit;
border-bottom-width: initial;
border-bottom-width: unset;

初始值	medium
适用元素	all elements. It also applies to ::first-letter.
是否是继承属性	否
计算值	the absolute length or 0 if border-bottom-style is none or hidden
Animation type	a length

Syntax

Values

<br-width>

定义边框宽度，取值为非负的宽度值<length>或关键字。 如果是关键字的话，其取值必须是以下之一：

thin		细边框
medium		中等边框
thick		粗边框

Note: 因为规范没有具体定义每个关键字对应的宽度值，所以实际显示效果依赖于实现。但是宽度值的取值一定遵循 thin ≤ medium ≤ thick 的规律且在单文档中是常数。

Formal syntax

<line-width>
where 
<line-width> = <length> | thin | medium | thick

Example

HTML

<div>Element 1</div>
<div>Element 2</div>

CSS

div {
  border: 1px solid red;
  margin: 1em 0;
}

div:nth-child(1) {
  border-bottom-width: thick;
}
div:nth-child(2) {
  border-bottom-width: 2em;
}

Result

Specifications

Specification	Status	Comment
CSS Backgrounds and Borders Module Level 3 border-bottom-width	Candidate Recommendation	No significant change.
CSS Level 2 (Revision 1) border-bottom-width	Recommendation	No significant change.
CSS Level 1 border-bottom-width	Recommendation	Initial definition.

Browser compatibility

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The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

See also

• The other border-width-related CSS properties: border-left-width, border-right-width, border-top-width, and border-width.
• The other border-bottom-related CSS properties: border, border-bottom, border-bottom-style, and border-bottom-color.