.mi-back-to-top {
    position: fixed;
    bottom: 30px;
    left: 20px;
    display: none;
    background-color: #2e323e;
    color: #fff;
    font-size: 24px;
    padding: 10px 15px;
    border-radius: 8px;
    text-decoration: none;
    z-index: 9999;
    box-shadow: 0 2px 6px rgba(0,0,0,.3);
    transition: background .3s ease;
}

.mi-back-to-top:hover {
    background-color: #444;
}