水平垂直居中
<!DOCTYPE html>
<html>
<title>水平垂直居中</title>
<head>
<style type="text/css">
.outer {
height: 200px;
width: 200px;
background: tomato;
margin: 10px;
float: left;
position: relative;
}
.inner {
height: 100px;
width: 100px;
background: black;
}
.inner1 {
position: absolute;
top: 50%;
left: 50%;
margin-top: -50px;
margin-left: -50px;
}
.inner2 {
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
margin: auto;
}
.outer3 {
display: flex;
justify-content: center;
align-items: center;
}
.inner4 {
top: 50%;
left: 50%;
transform: translate(-50%,-50%);
position: absolute;
}
</style>
</head>
<body>
<div class="outer outer1">
<div class="inner inner1"></div>
</div>
<div class="outer outer2">
<div class="inner inner2"></div>
</div>
<div class="outer outer3">
<div class="inner inner3"></div>
</div>
<div class="outer outer4">
<div class="inner inner4"></div>
</div>
</body>
</html>