<!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>垂直水平居中</title>
</head>
<style>
/* .box {
width: 500px;
height: 500px;
background-color: pink;
display: grid;
} */
/* .box {
width: 500px;
height: 500px;
background-color: pink;
position: relative;
} */
/* .box {
width: 500px;
height: 500px;
background-color: pink;
display: flex;
justify-content: center;
align-items: center;
} */
/* .modal {
width: 50px;
height: 50px;
background-color: forestgreen;
position: absolute;
margin: auto;
top: 0;
left: 0;
right: 0;
bottom: 0;
} */
/* .modal {
width: 50px;
height: 50px;
position: absolute;
left: 50%;
top: 50%;
margin-left: -25px;
margin-top: -25px;
background-color: green;
} */
/* .modal {
position: absolute;
left: 50%;
top: 50%;
transform: translate(-50%, -50%);
background-color: green;
} */
/* .modal {
background-color: green;
align-self: center;
justify-self: center;
} */
</style>
<body>
<section class="box">
<div class="modal">1232112312312321311231313</div>
</section>
<script>
let first = `子元素宽高固定的情况:宽高一半；2利用margin auto`;
let second = `利用margin auto`;
let third = `子元素宽高未知的情况`;
let fourthly = `flex布局`;
let fifth = `grid布局`;
</script>
</body>
</html>
