.renobtn {
    position: relative;
max-width:420px;
margin:0 auto;
text-align:center;
}

.renobtn img {
    transition: opacity 0.5s;
}
.renobtn:hover img:first-of-type {
    opacity: 0;
}
.renobtn img:last-of-type {
    position: absolute;
    top: 0px;
    left: 50%;
   transform: translateX(-50%);
    opacity: 0;
}
.renobtn:hover img:last-of-type {
    opacity: 1;
}