居中对齐
运行效果：
代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>hover宽度增长</title>
<style>
*{
padding: 0;
margin: 0;
}
#com{
width: 400px;
height:400px;
background:#ccc;
margin: 0 auto;
/*position: absolute;*/
}
#dq{
width: 100px;
height: 200px;
background-color: #f00;
position:relative;
left: 50%;
top: 50%;
transform:translate(-50%,-50%);
}
p{
height:200px;
background-color: blue;
}
</style>
</head>
<body>
<div id="com">
<div id="dq"></div>
<p></p>
</div>
</body>
</html>