#volver {   
    opacity: 0.5;
    background-color: red;
    border-radius: 0% 100% 0% 100% / 0% 0% 100% 100% ;
    padding: 10px;
    border: 0;
    position: fixed;
    top: 0;
    right: 0;
    color: white;
    transition: all 0.3s ease-out;
}

#iconoVolver{
    position: relative;
    bottom: 5px;
    left: 5px;
    font-size: 25px;
}
.sinEstilo {
    text-decoration: none;
    color: black;
}

#volver:hover {
    padding: 20px;
    opacity: 1;
    scale: 1.2;
}