@media only screen and (max-width: 600px) {
    /* For phone: */
    main {
        min-width: 75%;
        max-width: 75%;
    }
}
@media only screen and (min-width: 600px) {
    /* For tablet: */
    main {
        max-width: 25%;
    }
}

@media only screen and (min-width: 768px) {
    /* For desktop: */
    main {
        max-width: 25%;
    }
}