body {
    margin: 0;
}


@media only screen and (max-width: 768px) {
    .bg {
        /* The image used */
        background-image: url("https://marcosolar.com.br/background-mobile.png");
    
        /* Full height */
        height: 100%; 
    
        /* Center and scale the image nicely */
        background-position: center;
        background-repeat: no-repeat;
        background-size: contain;
    }    
}

@media only screen and (min-width: 768px) {
    .bg {
        /* The image used */
        background-image: url("https://marcosolar.com.br/background.png");
    
        /* Full height */
        height: 100%; 
    
        /* Center and scale the image nicely */
        background-position: center;
        background-repeat: no-repeat;
        background-size: contain;
    }    
}