.imagen--principal{
     background-image: url(../assets/img/portfolio/toner/generico-compatible.jpg);
     background-repeat: no-repeat;
     background-size: cover;
     width: 100%;
     height: 100%;
    }
    
    @media (min-width: 768px){
        .imagen--principal{
            background-image: url(../assets/img/portfolio/toner/generico-compatible.jpg);
            background-repeat: no-repeat;
            background-size: cover;
            width: 100%;
            height: 100%;
           } 
    }