先上张图
1.接着我是在这里样式就是父元素(.box)和子元素(.content)的属性都是:
box-sizng:border-box;
2.父元素设置padding值,边框,然后子元素的宽度为父元素的100%
3.事实证明子元素的宽度只和父元素的content宽度一样宽
具体详细代码
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
div{
box-sizing: border-box;
}
.box{
width: 200px;
height: 200px;
background-color:blue;
border: 1px solid red;
padding: 20px;
margin: 0 auto;
}
.content{
background-color: red;
width: 100%;
height:100px;
}
</style>
</head>
<body>
<div class='box'>
<!-- <div></div> -->
<div class="content">我是内容</div>
</div>
</body>
</html>