html,body{
	width: 100%;
	height: 100%;
	
}
.bg{
	width: 100%;
	height: 100%;
	background: url(http://qiniu.hixiaoluwenwen.com/PC/images/bg-class.png) no-repeat;
	background-size: 100% ;
	position: relative;
}
.big , .small{
	width: 20%;
	position: absolute;
}
.big {
	top: 20%;
	right: 15%;
	cursor: pointer;
}
.small {
	top: 40%;
	right: 40%;
	cursor: pointer;
}
.big img, .small img{
	width: 100%;
}

.back{
	width: 5%;
	position: absolute;
	top: 20px;
	right: 25px;
	cursor: pointer;
}
.back img{
	width: 100%;
	height: 100%;
}
@media screen and (max-width: 1920px) {
	html,body{
		width: 1920px;
		height: 1080px;
	}
}