<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>单位</title>
<style type="text/css">
/*
长度单位
像素px
百分比%
em
*/
.box{
width: 200px;
height: 200px;
background-color: red;
}
/*类选择器*/
.box1{
width: 100px;
height: 100px;
background-color: yellow;
}
.box2{
width: 25%;
height: 25%;
background-color: blue;
}
</style>
</head>
<body>
<div class="box">
<div class="box1">
<div class="box2"></div>
</div>
<div class="box2"></div>
</div>
</body>
</html>
