@keyframes alerta {
    0%   {opacity: 1;}
    50%  {opacity: 1;}
    80% {opacity: 0;}
    100% {opacity: 0;}
}

#alertaPopup {
    position: absolute;
    right: 10px;
    top: 10px;

    padding: 2px 8px 2px 8px;
    border: 1px solid black;
    background-color: red;
    color: white;

    animation-name: alerta;
    animation-duration: 10s;
    z-index: 102;
}