.custom_a{
width: 60px;
    height: 60px;
    display: block;
    /*background: #000;*/
    border-radius: 50%;
    position: relative;
}
.custom_a img{
 width: 50px;
    height: 50px;
    margin: auto;
    display: block;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);}
@media screen and (max-width: 1000px) {
   .custom_a {
        width: 40px;
        height: 40px;
    }
   .custom_a img {
        width: 35px;
        height: 35px;
    }
}