border-top-width

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

css 属性 border-top-width 是用于设置盒模型的上边框的宽度

尝试一下

Syntax

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

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

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

Values

<br-width>

上边框的宽度属性的有效值要么是一个具体的非负数，要么是一个关键字。如果是关键字，必须是一下几种：

thin A thin border
medium A medium border
thick A thick border

备注：Because the specification doesn't define the exact thickness denoted by each keyword, the precise result when using one of them is implementation-specific. Nevertheless, they always follow the pattern thin ≤ medium ≤ thick, and the values are constant within a single document.

Formal syntax

border-top-width = 
  <line-width>  

<line-width> = 
  <length [0,∞]>  |
  thin            |
  medium          |
  thick

Example

HTML

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

CSS

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

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

Result

Specifications

Specification
CSS Backgrounds and Borders Module Level 3
# the-border-width
初始值medium
适用元素所有元素. It also applies to ::first-letter.
是否是继承属性否
计算值绝对长度；或如果 border-top-style 的值为 none 或 hidden，则为 0
动画类型a length

Browser compatibility

BCD tables only load in the browser

See also