底部边距 | margin-bottom

margin-bottom

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。

/* <length> values */
margin-bottom: 10px;  /* An absolute length */
margin-bottom: 1em;   /* relative to the text size */
margin-bottom: 5%;    /* relative to the nearest block container's width */

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

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

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	no
Percentages	refer to the width of the containing block
适用媒体	visual
计算值	the percentage as specified or the absolute length
Animation type	a length
正规顺序	the unique non-ambiguous order defined by the formal grammar

语法

该margin-bottom属性被指定为关键字auto，或<length>或<percentage>。它的值可以是正值，零值或负值。

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参见margin。

正式语法

<length> | <percentage> | auto

示例

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

CSS的div来设置margin-bottom和height

.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;
}

容器和隔板的一些定义边缘的影响可以更清楚地看到

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

规范

Specification	Status	Comment
CSS Basic Box ModelThe definition of 'margin-bottom' in that specification.	Working Draft	No significant change
CSS TransitionsThe definition of 'margin-bottom' in that specification.	Working Draft	Defines margin-bottom as animatable.
CSS Level 2 (Revision 1)The definition of 'margin-bottom' in that specification.	Recommendation	Removes its effect on inline elements.
CSS Level 1The definition of 'margin-bottom' in that specification.	Recommendation	Initial definition

Browser compatibility

Feature	Chrome	Edge	Firefox (Gecko)	Internet Explorer	Opera	Safari (WebKit)
Basic support	1.0	(Yes)	1.0 (1.7 or earlier)	3.0	3.5	1.0 (85)
auto value	1.0	(Yes)	1.0 (1.7 or earlier)	6.0 (strict mode)	3.5	1.0 (85)

Feature	Android	Edge	Firefox Mobile (Gecko)	IE Phone	Opera Mobile	Safari Mobile
Basic support	1.0	(Yes)	1.0 (1)	6.0	6.0	1.0