css如何实现快速居中？
简单来说快速居中，就是给它的父级设置display: flex;属性，自身设置margin: auto;的属性
例如
<!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>Document</title>
<style>
* {
margin: 0px;
padding: 0px;
}
html,body {
width: 100%;
height: 100%;
display: flex;
}
.allitem{
width: 100px;
height: 100px;
background-color: yellow;
margin: auto;
}
.all {
width: 500px;
height: 500px;
background-color: red;
margin: auto;
display: flex;
}
</style>
</head>
<body>
<div class="all">
<div class="allitem">
</div>
</div>
</body>
</html>