（1）莫名其妙的居中
<style>
#outer{
width: 400px;
height: 400px;
border: 2px solid #333;
position: relative;
margin: 100px auto;
}
#inner{
width: 50%;
height: 50%;
background-color: #2e0088;
left: 0;
right: 0;
bottom: 0;
top: 0;
position: absolute;
margin: auto;
}
</style>
</head>
<body>
<div id="outer">
<div id="inner"></div>
</div>
</body>
（2）absolute+translate
<style>
#outer{
width: 400px;
height: 400px;
border: 2px solid #333;
position: relative;
margin: 100px auto;
}
#inner{
width: 50%;
height: 50%;
background-color: #2e0088;
left: 50%;
top: 50%;
transform: translate(-100px,-100px);
position: absolute;
}
</style>
</head>
<body>
<div id="outer">
<div id="inner"></div>
</div>
</body>
css居中.PNG
（1）百度前端技术学院css居中
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
.box{
width: 400px;
height: 200px;
background-color: #ccc;
position: absolute;
left: 50%;
top: 50%;
margin-top: -100px;
margin-left: -200px;
overflow: hidden;
}
.box div{
position: absolute;
width: 100px;
height: 100px;
background-color: #fc0;
border-radius: 50%;
}
.box .left{
left: -50px;
top: -50px;
}
.box .right{
right: -50px;
bottom: -50px;
}
</style>
</head>
<body>
<div class="box">
<div class="left"></div>
<div class="right"></div>
</div>
</body>
</html>
image.png
最佳实践
* {
margin: 0;
padding: 0;
}
.main {
position: absolute;
width: 400px;
height: 200px;
background-color: #ccc;
top: 50%;
margin-top: -100px;
left: 50%;
margin-left: -200px;
}
.left-top-area {
width: 50px;
height: 50px;
border-radius: 0 0 50px 0;
position: absolute;
background-color: #FC0;
}
.right-bottom-area {
width: 50px;
height: 50px;
border-radius: 50px 0 0 0;
position: absolute;
background-color: #FC0;
right: 0;
bottom: 0;
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>task-04</title>
<link rel="stylesheet" href="styles/main.css">
</head>
<body>
<div class="main">
<div class="left-top-area"></div>
<div class="right-bottom-area"></div>
</div>
</body>
</html>
