box-sizing和定位 - - php.cn博客

box-sizing

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
            /* padding和border计算在width,height里 */
            box-sizing: border-box;
        }
        html {
            font-size: 10px;
        }
        .box {
            width: 20rem;
            height: 20rem;
            border: #000 solid 2px;
            background-color: lightblue;
        }
    </style>
</head>
<body>
    <div class="box">box</div>
</body>
</html>

定位

相对定位
相对于它在文档流中的原始位置进行定位
绝对定位
绝对定位元素脱离了文档流

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
        .box {
            /* position: relative; */
            /* position: absolute; */
            top: 5em;
            left: 10em;
            background-color: lightskyblue;
            width: 20rem;
            height: 4rem;
        }
    </style>
</head>
<body>
    <div class="box">box</div>
    <p>Hello</p>
</body>
</html>