* {
    border: 1px dashed black;
    box-sizing: border-box;
    margin: 0;
}

body {
    min-height: 99vh;
    display: flex;
    flex-direction: column;
}

main {
    flex-grow: 1;
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
}

main>section {
    flex-grow: 3;
}

main>aside {
    flex-grow: 1;
}

main>article {
    flex-basis: 33.3333%;

}

@media (min-width: 600px) {
    main {
        display: flex;
        flex-direction: row;
    }

    main>section {
        flex-grow: 1;
    }
}

@media (min-width: 768px) {
    main {
        width: 768px;
        margin: auto;
    }
}