块级元素水平，垂直居中的两种方式
方式一： 利用margin
<!DOCTYPE html>
<html>
<head>
<title>块级元素水平，垂直居中</title>
<meta charset="utf-8">
<style>
.wrapper {
height: 600px;
border: 1px solid gray;
}
.box {
width: 100px;
height: 100px;
background: gold;
margin: 250px auto 0;
}
</style>
</head>
<body>
<div class="wrapper">
<div class="box"></div>
</div>
</body>
</html>
方式二，利用定位及负边距
<!DOCTYPE html>
<html>
<head>
<title>块级元素水平，垂直居中</title>
<meta charset="utf-8">
<style>
.wrapper {
height: 600px;
border: 1px solid gray;
position: relative;
}
.box {
width: 100px;
height: 100px;
background: gold;
position: absolute;
left: 50%;
top: 50%;
margin-left: -50px;
margin-top: -50px;
}
</style>
</head>
<body>
<div class="wrapper">
<div class="box"></div>
</div>
</body>
</html>
