#box3{text-align:center;border:1px dotted red}
#mask{margin-top:20px}
.mask{
	/*position:relative;*/
	width:780px;
	height:200px;
	overflow:hidden;
	text-align:center;

}
.mask img{
	/*position:absolute;*/
	display:block;
	border:none;
	margin:auto;	
}