CSS 属性 inset-block-start 定义了元素的块首偏移，并根据元素的书写模式、行内方向和文本朝向对应至实体偏移。根据 {{CSSXref("writing-mode")}}、{{CSSXref("direction")}} 和 {{CSSXref("text-orientation")}} 所定义的值，此属性对应于 {{CSSXref("top")}}、{{CSSXref("right")}}、{{CSSXref("bottom")}} 或 {{CSSXref("left")}} 属性。

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

```css interactive-example-choice writing-mode: horizontal-tb;


```css interactive-example-choice
writing-mode: vertical-rl;

```css interactive-example-choice writing-mode: horizontal-tb; direction: rtl;


```css interactive-example-choice
writing-mode: vertical-lr;

```html interactive-example

I am absolutely positioned with inset-block-start: 50px

As much mud in the streets as if the waters had but newly retired from the face of the earth, and it would not be wonderful to meet a Megalosaurus, forty feet long or so, waddling like an elephantine lizard up Holborn Hill. 


```css interactive-example
#example-element {
  border: 0.75em solid;
  padding: 0.75em;
  position: relative;
  width: 100%;
  min-height: 200px;
  unicode-bidi: bidi-override;
}

#abspos {
  background-color: yellow;
  color: black;
  border: 3px solid red;
  position: absolute;
  inset-block-start: 50px;
  inline-size: 140px;
}

语法

/* 长度值 */
inset-block-start: 3px;
inset-block-start: 2.4em;

/* 包含块的宽度或高度的百分比 */
inset-block-start: 10%;

/* 关键词值 */
inset-block-start: auto;

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

取值

inset-block-start 属性的取值与 {{CSSXref("left")}} 属性相同。

形式定义

{{CSSInfo}}

形式语法

{{CSSSyntax}}

示例

设置块首偏移

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;
  position: relative;
  inset-block-start: 20px;
  background-color: #c8c800;
}

结果

{{EmbedLiveSample("设置块首偏移", 140, 140)}}