上边框宽度 | border-top-width
border-top-width
border-top-width CSS属性设置一个框的顶部边框的宽度。
/* 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;
| 初始值 | medium |
|---|---|
| 适用元素 | all elements. It also applies to ::first-letter. |
| 是否是继承属性 | no |
| 适用媒体 | visual |
| 计算值 | the absolute length or 0 if border-top-style is none or hidden |
| Animation type | a length |
| 正规顺序 | the unique non-ambiguous order defined by the formal grammar |
语法
值
<br-width>定义边界的宽度，可以是明确的非负值<length>或关键字。如果是关键字，则必须是以下值之一：
| thin | | A thin border |
|---|---|---|
| medium | | A medium border |
| thick | | A thick border |
注意：由于规范没有定义每个关键字所表示的精确厚度，因此使用其中一个关键字的精确结果是特定于实现的。尽管如此，它们总是遵循这个模式thin ≤ medium ≤ thick，价值在一个单一的文件中是不变的。
正式语法
<br-width>where
<br-width> = <length> | thin | medium | thick
示例
HTML
<div>Element 1</div>
<div>Element 2</div>
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;
}
结果
规范
| Specification | Status | Comment |
|---|---|---|
| CSS Backgrounds and Borders Module Level 3The definition of 'border-top-width' in that specification. | Candidate Recommendation | No significant change. |
| CSS Level 2 (Revision 1)The definition of 'border-top-width' in that specification. | Recommendation | No significant change. |
| CSS Level 1The definition of 'border-top-width' in that specification. | Recommendation | Initial definition. |
浏览器兼容性
| Feature | Chrome | Edge | Firefox | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|---|
| Basic Support | 1 | (Yes) | 1 | 4 | 3.5 | 1 |
| Feature | Android | Chrome for Android | Edge mobile | Firefox for Android | IE mobile | Opera Android | iOS Safari |
|---|---|---|---|---|---|---|---|
| Basic Support | 2.3 | ? | (Yes) | 1 | 6 | 11 | 1 |
另见
- 其他的
border-width相关的CSS属性：border-left-width，border-right-width，border-bottom-width，和border-width。
- 其他
border-top相关CSS属性：border，border-top，border-top-style，和border-top-color。
