顾名思义，“开门大吉”指的是鼠标悬浮在块内的时候出现开门效果，显示出底部的图片。
知识点：3d变形、透视、translate移动
效果图：
完整源代码
<!DOCTYPE html>
<html>
<head>
<title></title>
<style type="text/css">
*{
margin: 0;
padding: 0;
}
.bg{
width: 300px;
height: 200px;
margin:100px auto;
position: relative;
transition: all 0.6s;
perspective: 500px;
border:1px solid black;
background-image: url(images/bg.jpg);
-webkit-background-size: cover;
background-size: cover;
}
.left,
.right{
width:50%;
height:100%;
background-color: red;
position: absolute;
top:0;
transition: 1s;
}
.left{
left:0;
transform-origin: left center;
border-right:1px solid black;
}
.right{
right:0;
transform-origin: right center;
border-left:1px solid black;
}
.left:before,.right:before{
content: "";
width:20px;
height: 20px;
border:1px solid black;
border-radius: 10px;
position: absolute;
left:0;
}
.left:before{
transform: translate(127px,80px);
}
.right:before{
transform: translate(0px,80px);
}
.bg:hover .left{
transform: rotateY(-120deg);
}
.bg:hover .right{
transform: rotateY(120deg);
}
</style>
</head>
<body>
<div class="bg">
<div class="left"></div>
<div class="right"></div>
</div>
</body>
</html>