43.元素的层级 - 《CSS》

html:
代码：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="../css/reset.css">
    <link rel="stylesheet" href="../css/74元素的层级.css">
</head>
<body>
    <div class="box1"></div>
    <div class="box2"></div>
    <div class="box3"> </div>
</body>
</html>

css:
(1)所有的布局加了position:absolute;之后会提升层级
(2)当所有的布局都加了absolute之后,后面的会压在前面
(3)当加上z-index: x;数字越大越能提升层级
(4)当一个后代元素包含于祖先元素中时,无论祖先元素层级多高,后代元素都在它上面

代码:

.box1 {
    width: 300px;
    height: 300px;
    background-color: #bfa;
    position: absolute;
    z-index:1;
}

.box2 {
    width: 300px;
    height: 300px;
    background-color:rgba(255,0,240,0.3);
    position: absolute;
    top:150px;
    left: 150px;
    z-index:1;
}

.box3 {
    width: 300px;
    height: 300px;
    background-color:burlywood;
    position: absolute;
    top:300px;
    left:300px;
    z-index:0.1;
}

.box4 {
    width: 300px;
    height: 300px;
    background-color: seagreen;
    position: absolute;
    top: 450px;
    left: 450px;
}