.contenedor{
    width: 100%;
    text-align: center;
    display: flex;
    height: 100vh;
    align-items: center;
}
.contenedor img{
    width: 50%;
    margin: 0 auto;
}
@media only screen and (max-width: 768px){
    .contenedor img{
        width: 100%;
    }
}