.pic_list li { float: left; margin: 0 0 10px 20px; width: 181px; height: 254px;}
.pic_list li .img_box { width: 174px; height:224px;}
.pic_list li .img_box img{width: 174px;height: 224px;}
@media only screen and (max-width:768px){
 .pic_list li{ width:162px; height:201px;}
 .pic_list li .img_box{ width:100%; height:auto; box-sizing:border-box}
 .pic_list li .img_box img{ width:100%; height:auto;}
 
}
@media only screen and (max-width:640px){
 .pic_list li{ width:181px; height:254px; margin:0 auto; float:none; display:block;}

 
}