<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title>Several methods for CSS to achieve centering</title>
</head>
<body>
<div class="parent">
<div class="child"></div>
</div>
<style>
.parent{
width: 200px;
height: 200px;
background: #ccc;
position: relative;
/*1, flex layout implementation. Center justify-content horizontally, center align-items vertically*/
display:flex;
justify-content: center;
align-items: center;
}
.child{
width: 50px;
height: 50px;
background: #aaa;
position: absolute;
/*2, margin:auto implementation. Full center: auto, horizontal center: 0 auto, vertical center: auto 0*/
/*left:0;
top: 0;
bottom: 0;
right: 0;
margin: auto;*/
/*3, Transforms deformation implementation. The left and top values are the parent percentages, and the translate values are their own percentages*/
/*left: 50%;
top: 50%;
transform: translate(-50%,-50%);*/
/*4, the margin negative spacing is realized. The negative value of margin is -1/2*/ of width and height
/*left: 50%;
top: 50%;
margin-left: -25px;
margin-top: -25px;*/
}
</style>
</body>
</html>