z-index

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.

CSS z-index 属性设置定位元素及其后代元素或 flex 项目的 Z 轴顺序。z-index 较大的重叠元素会覆盖较小的元素。

尝试一下

z-index: auto; 
z-index: 1; 
z-index: 3; 
z-index: 5; 
z-index: 7; 
<section class="default-example container" id="default-example"> <div id="example-element">Change my z-index</div> <div class="block blue position1">z-index: 6</div> <div class="block blue position2">z-index: 4</div> <div class="block blue position3">z-index: 2</div> <div class="block red position4">z-index: auto</div> <div class="block red position5">z-index: auto</div> <div class="block red position6">z-index: auto</div> </section> 
#example-element { top: 15px; left: 15px; width: 180px; height: 230px; position: absolute; /* center the text so it is visible even when z-index is set to auto */ line-height: 215px; font-family: monospace; background-color: #fcfbe5; border: solid 5px #e3e0a1; z-index: auto; color: black; } .container { display: inline-block; width: 250px; position: relative; } .block { width: 150px; height: 50px; position: absolute; font-family: monospace; color: black; } .blue { background-color: #e5e8fc; border: solid 5px #112382; /* move text to the bottom of the box */ line-height: 55px; } .red { background-color: #fce5e7; border: solid 5px #e3a1a7; } .position1 { top: 0; left: 0; z-index: 6; } .position2 { top: 30px; left: 30px; z-index: 4; } .position3 { top: 60px; left: 60px; z-index: 2; } .position4 { top: 150px; left: 0; z-index: auto; } .position5 { top: 180px; left: 30px; z-index: auto; } .position6 { top: 210px; left: 60px; z-index: auto; }

对于定位盒子（即 position 属性值非 static 的盒子），z-index 属性会指定：

  1. 盒子在当前层叠上下文中的层叠等级。
  2. 盒子是否会创建局部层叠上下文。

语法

css
/* 关键字值 */ z-index: auto; /* 整数值 */ z-index: 0; z-index: 3; z-index: 289; z-index: -1; /* 使用负值降低优先级 */ /* 全局值 */ z-index: inherit; z-index: initial; z-index: unset;

z-index 属性可以被设置为关键字 auto 或 <integer>。

取值

auto

盒子不会创建一个新的局部层叠上下文。盒子在当前层叠上下文的层叠等级是 0。

<integer>

盒子在当前层叠上下文的层叠等级就是 <integer> 的值。盒子还会创建一个局部层叠上下文。这意味着该元素的后代元素不会和该元素的外部元素比较 z-index。

形式定义

初始值auto
适用元素positioned elements
是否是继承属性否
计算值as specified
动画类型an integer
Creates stacking context是

形式语法

z-index = 
 auto |
 <integer> |
 inherit

示例

视觉上的分层元素

HTML

html
<div class="wrapper"> <div class="dashed-box">Dashed box</div> <div class="gold-box">Gold box</div> <div class="green-box">Green box</div> </div>

CSS

css
.wrapper { position: relative; } .dashed-box { position: relative; z-index: 1; border: dashed; height: 8em; margin-bottom: 1em; margin-top: 2em; } .gold-box { position: absolute; z-index: 3; /* put .gold-box above .green-box and .dashed-box */ background: gold; width: 80%; left: 60px; top: 3em; } .green-box { position: absolute; z-index: 2; /* put .green-box above .dashed-box */ background: lightgreen; width: 20%; left: 65%; top: -25px; height: 7em; opacity: 0.9; }

结果

规范

Specification
Cascading Style Sheets Level 2
# z-index

浏览器兼容性

参阅