CSS 属性 border-block-start-width 定义了元素的逻辑块首的边框宽度，并根据元素的书写模式、行内方向和文本朝向对应至实体边框宽度。根据 {{CSSXref("writing-mode")}}、{{CSSXref("direction")}} 和 {{CSSXref("text-orientation")}} 所定义的值，此属性对应于 {{CSSXref("border-top-width")}}、{{CSSXref("border-right-width")}}、{{CSSXref("border-bottom-width")}} 或 {{CSSXref("border-left-width")}} 属性。

{{InteractiveExample("CSS Demo: border-block-start-width")}}

```css interactive-example-choice border-block-start-width: thick; writing-mode: horizontal-tb;


```css interactive-example-choice
border-block-start-width: thick;
writing-mode: vertical-rl;

```css interactive-example-choice border-block-start-width: 4px; writing-mode: horizontal-tb;


```css interactive-example-choice
border-block-start-width: 4px;
writing-mode: vertical-lr;

```html interactive-example

This is a box with a border around it. 


```css interactive-example
#example-element {
  background-color: palegreen;
  color: #000;
  border: 0 solid crimson;
  padding: 0.75em;
  width: 80%;
  height: 100px;
  unicode-bidi: bidi-override;
}

语法

/* 边框宽度值 */
border-block-start-width: 5px;
border-block-start-width: thick;

/* 全局值 */
border-block-start-width: inherit;
border-block-start-width: initial;
border-block-start-width: revert;
border-block-start-width: revert-layer;
border-block-start-width: unset;

与此相关的属性有 {{CSSXref("border-block-end-width")}}、{{CSSXref("border-inline-start-width")}} 和 {{CSSXref("border-inline-end-width")}}，这些属性定义了元素其他边框的宽度。

{{CSSInfo}}

取值

  • <'border-width'>
    • : 边框宽度。见 {{CSSXref("border-width")}}。

形式定义

{{CSSInfo}}

形式语法

{{CSSSyntax}}

示例

竖排文本的边框宽度

HTML

<div>
  <p class="exampleText">示例文本</p>
</div>

CSS

div {
  background-color: yellow;
  width: 120px;
  height: 120px;
}

.exampleText {
  writing-mode: vertical-lr;
  border: 1px solid blue;
  border-block-start-width: 5px;
}

结果

{{EmbedLiveSample("竖排文本的边框宽度", 140, 140)}}