div{
box-sizing:border-box;
width:200px;
padding:20px;
border: 1px solid red;
}
This css means that the div width is 200px, the border is 1px, the left and right margins are 20px, and the time content width is Adaptive, it is 200-2-20*2=158px;
If the value of box-sizing is content-box, it means that the width of the content area is set, not the div box Width;
Browser compatibility:
ie8 and above support this attribute, firefox needs to add the browser manufacturer prefix -moz-, low version IOS and Android browsing You also need to add -webkit-
*,*:before,*:after{
-moz-box-sizing:border-box;
-webkit- box-sizing:border-box;
box-sizing:border-box;
}