body {
    margin: 0;
    padding: 0;
    background-color: #3a3c42;
}

main img {
    display: block;
    height: auto;
    width: 100%;
}

/* media queries */
@media screen and (max-width: 640px) {
    .desktop {display: none;}
}

@media screen and (min-width: 641px) {
    .mobile {display: none;}
}