margin-bottom

Baseline Widely available *

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

* Some parts of this feature may have varying levels of support.

Summary

The effect of the CSS margin-bottom property on the element box

CSS 的 margin-bottom 属性用于设置元素的底部外边距，允许设置负数值。一个正数值将让它相对于正常流与邻近块更远，而负数值将使得更近。

该属性对于*不可替代 (non-replaced 元素在规范中有概念，请自行搜索)*的行级元素没有效果，比如： <tt> 或者 <span>.

初始值0
适用元素all elements, except elements with table display types other than table-caption, table and inline-table. It also applies to ::first-letter.
是否是继承属性否
Percentagesrefer to the width of the containing block
计算值the percentage as specified or the absolute length
动画类型a length

语法

css
/* <length> values */
margin-bottom: 10px; /* 一个绝对的长度值 */
margin-bottom: 1em; /* A length relative to the text size */
margin-bottom: 5%; /* A margin relative to the nearest block container's width */

/* Keyword values */
margin-bottom: auto;

/* Global values */
margin-bottom: inherit;
margin-bottom: initial;
margin-bottom: unset;

值

<length>

定义了一个确定的宽度值，参见 <length> 以了解更多可能的值。

<percentage>

<percentage> 始终与包含该元素的容器宽度有关。

auto

由浏览器自己选择一个合适的值。参见 margin。

形式语法

margin-bottom = 
  <length-percentage>  |
  auto                 |
  <anchor-size()>      

<length-percentage> = 
  <length>      |
  <percentage>  

<anchor-size()> = 
  anchor-size( [ <anchor-name> || <anchor-size> ]? , <length-percentage>? )  

<anchor-name> = 
  <dashed-ident>  

<anchor-size> = 
  width        |
  height       |
  block        |
  inline       |
  self-block   |
  self-inline

示例

HTML

html
<div class="container">
  <div class="box0">Box 0</div>
  <div class="box1">Box 1</div>
  <div class="box2">Box one's negative margin pulls me up</div>
</div>

CSS

用于设置 div 的 margin-bottom 和 height 的 CSS 代码

css
.box0 {
  margin-bottom: 1em;
  height: 3em;
}
.box1 {
  margin-bottom: -1.5em;
  height: 4em;
}
.box2 {
  border: 1px dashed black;
  border-width: 1px 0;
  margin-bottom: 2em;
}

为了使 margin 产生的影响更明显，添加了一些 container 和 div 的样式定义

css
.container {
  background-color: orange;
  width: 320px;
  border: 1px solid black;
}
div {
  width: 320px;
  background-color: gold;
}

规范

Specification
CSS Box Model Module Level 3
# margin-physical

浏览器兼容性