#back-to-top {
    position: fixed;
    bottom: 30px;
    right: 110px;
    z-index: 99;
    width: 45px;
    height: 45px;
    text-align: center;
    line-height: 30px;
    font-size: 18px;
    border: none;
    outline: none;
    background: gray;
    color: #444;
    cursor: pointer;
    text-decoration: none;
    -ms-border-radius: 4px;
    border-radius: 4px;
    -ms-transition: opacity 0.2s ease-out;
    -o-transition: opacity 0.2s ease-out;
    -webkit-transition: opacity 0.2s ease-out;
    transition: opacity 0.2s ease-out;
    -ms-opacity: 0;
    opacity: 0;
    padding: 5px;
}

    #back-to-top:hover {
        background: #e9ebec;
    }

    #back-to-top.show {
        -ms-opacity: 1;
        opacity: 1;
    }