.sub ul {text-align:center;}
.sub ul li {display:inline-block;width:45%;margin:20px 10px;}
.sub ul li span {display:block;font-size:16px;padding:10px 0;background:#3978b3;color:#fff;}

.sub ul li img{width:100%;} 
/* tablet */
@media screen and (min-width:769px) and (max-width:991px){
}

/* mobile */
@media screen and (max-width:768px){
    .sub ul li {width:100%;margin:inherit;}
}