Box model 1
<!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>
#one{
height: 100px;
width: 200px;
background: green;
}
#a{
width: 50%;
height: 100%;
background: blue;
float: left;
}
#b{
width: 50%;
height: 100%;
background: gray;
float: right;
padding: 20px;
}
</style>
</head>
<body>
<div id="one">
<div id="a"></div>
<div id="b"></div>
</div>
</body>
</html>
The above is the new box model. If paddingborder is added, the parent div will not be able to accommodate these added new attributes and expand outward.
Box model 2
If we convert the above box model into an old-fashioned IE browser and store it inside, we only need to add the following CSS code to change the properties of the box model
box-sizing: border-box;
box-sizing: border-box ;
