#Boton-ir-arriba {
    display: none;
    z-index: 1010;
    width: 48px;
    height: 48px;
    position: fixed;
    bottom: 25px;
    right: 25px;
    cursor: pointer;
    overflow: hidden;
    color: #fff;
    text-align: center;
    line-height: 48px;
    border-radius: 0;
    background-color: black;
}

#Boton-ir-arriba i {
    position: relative;
    font-family: FontAwesome;
    font-weight: 400;
    opacity: .8;
    transition: opacity .17s ease;
    width: 40px;
    height: 40px;
    display: inline-block;
    line-height: 48px;
}

#Boton-ir-arriba:hover i,
.nav-active #Boton-ir-arriba i {
    opacity: 1;
}