水平居中
三种方法,参考:


<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="utf-8">
    <meta name="renderer" content="webkit">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title></title>
    <style> * {
     margin: 0; padding: 0; } div {
     // 一: width: 200px; height: 200px; background: blue; position: absolute; left: 50%; /*弊端:不利于编码,需要口算宽度的一半*/ /*margin-left: -100px;*/ // 二: /*弊端:transform是新增属性,有的浏览器不支持,所以不利于兼容*/ transform: translateX(-50%); //三: /*在css3中新增了一个cala()函数,可以实现简单的运算*/ /*弊端:css3新增的,有的不支持*/ /*margin-left: calc(-200px / 2);*/ /*margin-left: calc(-200px / 0.5);*/ } </style>
</head>
<body>

<div></div>

</body>
</html>

效果:

水平,竖直方向居中,一种方法:

<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="utf-8">
    <meta name="renderer" content="webkit">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title></title>
    <style> * {
     margin: 0; padding: 0; } .father {
     width: 300px; height: 300px; background: red; position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); } .father .son {
     width: 200px; height: 200px; background: blue; position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); } </style>
</head>
<body>
<div class="father">
    <div class="son"></div>
</div>
</body>
</html>

效果: