bottom | CSS

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句法
形式定义
形式句法
范例
规范
浏览器兼容性
另请参阅
相关话题

bottom CSS property participates in setting the vertical position of a positioned element . It has no effect on non-positioned elements.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

The effect of bottom depends on how the element is positioned (i.e., the value of the position property):

When position is set to absolute or fixed ， bottom property specifies the distance between the element's bottom edge and the bottom edge of its containing block.
When position is set to relative ， bottom property specifies the distance the element's bottom edge is moved above its normal position.
When position is set to sticky ， bottom property is used to compute the sticky-constraint rectangle.
When position is set to static ， bottom property has no effect .

When both top and bottom are specified, position is set to absolute or fixed , and height is unspecified (either auto or 100% ) both the top and bottom distances are respected. In all other situations, if height is constrained in any way or position is set to relative ， top property takes precedence and the bottom property is ignored.

句法

/* <length> values */
bottom: 3px;
bottom: 2.4em;
/* <percentage>s of the height of the containing block */
bottom: 10%;
/* Keyword value */
bottom: auto;
/* Global values */
bottom: inherit;
bottom: initial;
bottom: unset;

值

<length>

A negative, null, or positive


<length>

that represents:

for absolutely positioned elements , the distance to the bottom edge of the containing block.
for relatively positioned elements , the distance that the element is moved above its normal position.

<percentage>


<percentage>

of the containing block's height.

auto

Specifies that:

for absolutely positioned elements , the position of the element is based on the top property, while height: auto is treated as a height based on the content; or if top is also auto , the element is positioned where it should vertically be positioned if it were a static element.
for relatively positioned elements , the distance of the element from its normal position is based on the top property; or if top is also auto , the element is not moved vertically at all.

inherit

Specifies that the value is the same as the computed value from its parent element (which might not be its containing block). This computed value is then handled as if it were a


<length>


<percentage>

，或


auto

关键词。

形式定义

初始值	`auto`
适用于	positioned elements
继承	no
百分比	refer to the height of the containing block
计算值	if specified as a length, the corresponding absolute length; if specified as a percentage, the specified value; otherwise, `auto`
动画类型	a length , percentage or calc();

形式句法

<length> | <percentage> | auto

范例

Absolute and fixed positioning

This example demonstrates the difference in behavior of the bottom property, when position is absolute versus fixed .

HTML

<p>This<br>is<br>some<br>tall,<br>tall,<br>tall,<br>tall,<br>tall<br>content.</p>
<div class="fixed"><p>Fixed</p></div>
<div class="absolute"><p>Absolute</p></div>

CSS

p {
  font-size: 30px;
  line-height: 2em;
}
div {
  width: 48%;
  text-align: center;
  background: rgba(55,55,55,.2);
  border: 1px solid blue;
}
.absolute {
  position: absolute;
  bottom: 0;
  left: 0;
}
.fixed {
  position: fixed;
  bottom: 0;
  right: 0;
}

结果

规范

规范	状态	注释
CSS Positioned Layout Module Level 3 The definition of 'bottom' in that specification.	工作草案	Adds behavior for sticky positioning.
CSS Level 2 (Revision 1) The definition of 'bottom' in that specification.	推荐	初始定义。

浏览器兼容性

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`bottom`	Chrome 完整支持 1	Edge 完整支持 12	Firefox 完整支持 1	IE 完整支持 5 注意事项完整支持 5 注意事项注意事项 In Internet Explorer versions before 7, when both `top` and `bottom` are specified, the element position is overconstrained and the `top` property has precedence; the computed value of `bottom` is set to `-top` , while its specified value is ignored.	Opera 完整支持 6	Safari 完整支持 1	WebView Android 完整支持 ≤37	Chrome Android 完整支持 18	Firefox Android 完整支持 4	Opera Android 完整支持 14	Safari iOS 完整支持 1	Samsung Internet Android 完整支持 1.0

图例

完整支持
见实现注意事项。

另请参阅

inset , the shorthand for all related properties: top , bottom , left ，和 right
The mapped logical properties: inset-block-start , inset-block-end , inset-inline-start ，和 inset-inline-end and the shorthands inset-block and inset-inline
position

元数据

最后修改： Aug 31, 2020

CSS
CSS 参考
CSS Positioning
指南
1. Understanding CSS z-index
特性
1. bottom
2. clear
3. float
4. left
5. position
6. right
7. top
8. z-index

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句法

值