.cust-btn{
    width: 30px;
    height: 30px;
    line-height: 30px;
    text-align: center;
    font-size: 15px;
    position: absolute;
    top: 50%;
    margin-top: -20px;
    z-index: 100;
    border-radius: 100px;
    border: solid 1px #666;
    background-color: rgb(0,0,0, .4);
    color: #FFF;
}

.cust-btn.prev{
    left: -15px;
}
.cust-btn.next{
    right: -15px;
}