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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 2015年7月.
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
border-top-width: thick;
border-top-width: 2em;
border-top-width: 4px;
border-top-width: 2ex;
border-top-width: 0;
<section class="default-example" id="default-example">
<div class="transition-all" id="example-element">
This is a box with a border around it.
</div>
</section>
#example-element {
background-color: palegreen;
color: #000;
border: 0 solid crimson;
padding: 0.75em;
width: 80%;
height: 100px;
}
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:
thinA thin border mediumA medium border thickA 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
[フレーム]
Specifications
| Specification |
|---|
| CSS Backgrounds and Borders Module Level 3 # 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
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See also
- The other border-width-related CSS properties:
border-left-width,border-right-width,border-bottom-width, andborder-width. - The other border-top-related CSS properties:
border,border-top,border-top-style, andborder-top-color.