css上下左右居中

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        html,body{
            width: 100%;
            height: 100%;
            font-size: 16px;
        }

        *{margin: 0;padding: 0;}

        .box1{
            width: 200px;height: 200px;
            background: #eee;
            margin-top: 10px;

            /*定位居中*/
            position: relative;

        }
        .box2{
            width: 200px;height: 200px;
            background: #eee;
            margin-top: 10px;

            /*margin居中*/
            position: relative;
        }
        .box3{
            width: 200px;height: 200px;
            background: #eee;
            margin-top: 10px;

            /*inline居中*/
            text-align: center;

        }
        /*定位+transform居中*/
        .box1 div{border: 1px solid #000;position: absolute;left: 50%;top: 50%;transform: translate(-50%,-50%)}

        /*margin居中*/
        .box2 div{border: 1px solid #000;position: absolute;left: 0;top: 0;bottom: 0;right: 0;margin:auto;width: 100px;height: 50px}

        /*inline居中*/
        .box3 div{border: 1px solid #000;display: inline-block;vertical-align: middle;}
        .box3:before{content: '';  display: inline-block;  height: 100%;  vertical-align: middle;}
    </style>
</head>
<body>
<div class="box1">
    <div>我想居中</div>
</div>
<div class="box2">
    <div>我想居中</div>
</div>
<div class="box3">
    <div>我想居中</div>
</div>
</body>
</html>
demo: https://controllerone.github.io/test/