UIView *backView=[[UIView alloc]initWithFrame:CGRectMake(0, 0, 100, 92)];
backView.layer.shadowColor=COLOR(253, 249, 204).CGColor;
backView.layer.shadowOffset = CGSizeMake(0,4);
backView.layer.shadowOpacity = 0.8;//阴影透明度，默认0
backView.layer.shadowRadius = 4;//阴影半径，默认3
