box-sizing的用法

    默认情况下设置盒子的width是指内容区域,所以在设置边框会使得盒子往外扩张,如果要让css设置的width就是盒子最终的宽度,那么就要设置box-sizing:border-box,
    这样添加border后,盒子会往内扩张,也就是设置的width就是盒子最终大小,box-sizing: content-box 是它的默认值
 
　1.默认情况 
<!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>
</head>

<style>
div{
    background-color: aqua;
    width: 500px;
    height: 500px;
    border: 10px solid gold;
    padding: 20px;
    box-sizing: content-box;
    margin: 0 auto;
}




</style>
<body>
    <div>pppp</div>
</body>
</html>

效果如下:

　　

 

            2.box-sizing:border-box

<!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>
</head>
<style>
div{
    background-color: aqua;
    width: 500px;
    height: 500px;
    border: 10px solid gold;
    padding: 20px;
    box-sizing: border-box;
    margin: 0 auto;
}




</style>
<body>
    <div>pppp</div>
</body>
</html>

效果如下:

 

posted @ 2019-02-15 10:34  yangxiaohui227  阅读(214)  评论(0)    收藏  举报