<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<style>
.box1{
width: 200px;
height: 100px;
background-color: red;
position: relative;
overflow: hidden;
}
.box2{
width: 100px;
height: 200px;
background-color: green;
position: absolute;
top: 20px;
left: 20px;
}
</style>
</head>
<body>
<div class="box0">
<div class="box1">
<div class="box2"></div>
</div>
</div>
</body>
</html>
子元素相对父元素定位没有显示完全，解决办法就是：从最上祖先元素往下找，找到一个合适且没有设置overflow：hideen的元素，以此以此元素做参考点。必须是一个没。overflow：hidden的祖先元素啊，这样才不会挡住绝对定位的子元素。而且要从上往下，不然你得把找到元素的所有祖先元素设置的overflow：hideen全删掉才行，这在开发过程中肯定是不行的
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<style>
.box0{
position: relative;
}
.box1{
width: 200px;
height: 100px;
background-color: red;
/*position: relative;*/
overflow: hidden;
}
.box2{
width: 100px;
height: 200px;
background-color: green;
position: absolute;
top: 20px;
left: 20px;
}
</style>
</head>
<body>
<div class="box0">
<div class="box1">
<div class="box2"></div>
</div>
</div>
</body>
</html>