overflow-block
==============

CSS 属性 **`overflow-block`** 设置了当内容溢出盒的块首和块末侧时所显示的内容。可以不显示，或者显示滚动条或溢出内容。

**备注：**`overflow-block` 属性根据文档的书写模式对应于 `overflow-y` 或 `overflow-x`。

语法
--


```css
/\* 关键词值 \*/
overflow-block: visible;
overflow-block: hidden;
overflow-block: scroll;
overflow-block: auto;

/\* 全局值 \*/
overflow-block: inherit;
overflow-block: initial;
overflow-block: revert;
overflow-block: revert-layer;
overflow-block: unset;
```


`overflow-block` 属性可指定为下列关键词之一。

### 取值

`visible`

不裁剪内容且可在内边距盒的块首和块末侧外渲染内容。

`hidden`

若内边距盒在块向尺度上无法容纳内容则裁剪内容。不提供滚动条。

`scroll`

若内边距盒在块向尺度上无法容纳内容则裁剪内容。无论内容是否被裁剪，浏览器均显示滚动条。（由此可阻止滚动条在内容变化时显示或消失。）打印机仍可能打印溢出内容。

`auto`

取决于用户代理。若内边距盒可以容纳内容，则与 `visible` 表现相同，但仍建立新的块格式化上下文。若内容溢出则桌面浏览器提供滚动条。

形式定义
----

|  |  |
| --- | --- |
| 初始值 | `auto` |
| 适用元素 | Block-containers, flex containers, and grid containers |
| 是否是继承属性 | 否 |
| 计算值 | as specified, except with `visible`/`clip` computing to `auto`/`hidden` respectively if one of `overflow-x` or `overflow-y` is neither `visible` nor clip |
| Animation type | discrete |

形式语法
----
```

overflow-block =   
  visible  |  
  hidden   |  
  clip     |  
  scroll   |  
  auto       
  
```

示例
--

### HTML


```html
<ul>
  <li>
    <code>overflow-block:hidden</code>——在盒外隐藏文本
    <div id="div1">
      Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
      tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim
      veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea
      commodo consequat. Duis aute irure dolor in reprehenderit in voluptate
      velit esse cillum dolore eu fugiat nulla pariatur.
    </div>
  </li>

  <li>
    <code>overflow-block:scroll</code>——总是添加滚动条
    <div id="div2">
      Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
      tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim
      veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea
      commodo consequat. Duis aute irure dolor in reprehenderit in voluptate
      velit esse cillum dolore eu fugiat nulla pariatur.
    </div>
  </li>

  <li>
    <code>overflow-block:visible</code>——按需在盒外显示文本
    <div id="div3">
      Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
      tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim
      veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea
      commodo consequat. Duis aute irure dolor in reprehenderit in voluptate
      velit esse cillum dolore eu fugiat nulla pariatur.
    </div>
  </li>

  <li>
    <code>overflow-block:auto</code>——在多数浏览器上等价于 <code>scroll</code>
    <div id="div4">
      Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
      tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim
      veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea
      commodo consequat. Duis aute irure dolor in reprehenderit in voluptate
      velit esse cillum dolore eu fugiat nulla pariatur.
    </div>
  </li>
</ul>
```

### CSS


```css
#div1,
#div2,
#div3,
#div4 {
  border: 1px solid black;
  width: 250px;
  height: 100px;
}

#div1 {
  overflow-block: hidden;
  margin-bottom: 120px;
}
#div2 {
  overflow-block: scroll;
  margin-bottom: 120px;
}
#div3 {
  overflow-block: visible;
  margin-bottom: 120px;
}
#div4 {
  overflow-block: auto;
  margin-bottom: 120px;
}
```

### 结果

规范
--

| Specification |
| --- |
| CSS Overflow Module Level 3 # overflow-control |

浏览器兼容性
------

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参见
--

* 相关 CSS 属性：`text-overflow`、`white-space`、`overflow`、`overflow-inline`、`overflow-x`、`overflow-y`、`clip`、`display`
* CSS 逻辑属性
* 书写模式