<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>井</title>
<style>
.box {
300px;
margin: 100px;
overflow: hidden;
}
.item {
float: left;
100px;
height: 100px;
border: 1px solid #000;
border-right: 0;
border-bottom: 0;
margin-left: -1px;
margin-top: -1px;
}
</style>
</head>
<body>
<div class="box">
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
</div>
</body>
</html>
1、父元素设置宽度 每行控制几个
2、子元素boder，且border-right/border-bottom设为0。通过margin负距隐藏border-top/border-lelft