css元素水平垂直居中-优快云博客

本文链接：https://blog.youkuaiyun.com/weixin_44749729/article/details/108376646

margin 负间距

需父元素设置相对低位已知子元素宽高
relative ：相对于起始位置的定位，起始位置基于父元素

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id='app'>
        <div class="a">aaaa</div>
    </div>
</body>
<style>
    #app {
        position: relative;
        width: 400px;
        height: 400px;
        background-color: cornflowerblue;
    }

    .a {
        width: 200px;
        height: 200px;
        background: green;
        position: absolute;
        left: 50%;
        top: 50%;
        margin-left: -100px;
        margin-top: -100px;

    }
</style>

</html>

Transforms 变形

与上一种道理一样，不过不用知道宽高

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id='app'>
        <div class="a">aaaa</div>
    </div>
</body>
<style>
    #app {
        position: relative;
        width: 400px;
        height: 400px;
        background-color: cornflowerblue;
    }

    .a {
        background: green;
        position: absolute;
        left: 50%;
        /* 定位父级的50% */
        top: 50%;
        transform: translate(-50%, -50%);
        /*自己的50% */


    }
</style>

</html>

使用 flex 弹性布局

常用

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id='app'>
        <div class="a">aaaa</div>
    </div>
</body>
<style>
    #app {
        display: flex;
        width: 400px;
        height: 400px;
        background-color: cornflowerblue;
        justify-content: center;
        align-items: center;
    }

    .a {
        background-color: brown;
    }
</style>

</html>

绝对定位方法边距auto

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id='app'>
        <div class="a">aaaa</div>
    </div>
</body>
<style>
    #app {
        position: relative;
        width: 400px;
        height: 400px;
        background-color: cornflowerblue;
    }

    .a {
        width: 200px;
        height: 200px;
        background: red;
        position: absolute;
        left: 0;
        top: 0;
        bottom: 0;
        right: 0;
        margin: auto;
    }
</style>

</html>