垂直居中 - 简书

首先写个基本样式

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>index</title>
    <style>
      html,body {
            width: 100%;
            height: 100%;
            margin: 0;
            padding: 0;
        }
        .content {
            width: 300px;
            height: 300px;
            background: orange;
        }
    </style>
</head>
<body>
    <div class="content"></div>
</body>
</html>

1.display：flex实现

body{
            display: flex;
            align-items: center;
        }

2.display:absolute(已知元素高度)

 .content {
            width: 300px;
            height: 300px;
            background: orange;
            display:absolute;
            top:50%;
            margin-top:-150px;//向上移元素一半的距离
        }

3.display:absolute(未知元素高度)

.content {
            width: 300px;
            height: 300px;
            background: orange;
            display:absolute;
            top:50%;
            left:50%
             transform:translate(-50%,-50%);//向左向上移元素一半的距离
        }