<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
#wrap{
width: 800px;
border: 2px solid;
padding: 10px 0 ;
display: flex;
flex-flow: row nowrap;
justify-content: space-around;
align-items: flex-start;
margin: 0 auto;
}
.box{
width: 280px;
/*height: 200px;*/
/*background-color: pink;*/
margin: 10px;
}
.item{
width: 100%;
font-size: 100px;
text-align: center;
margin: 10px 0;
}
#back{
position: fixed;
right: 20px;
bottom: 70px;
cursor: pointer;
}
</style>
</head>
<body>
<!-- 三列瀑布流 -->
<div id="wrap">
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
<div id="back">