html {
    height: 100%;
}

html * {
    box-sizing: border-box;
}

body {
    font-family: Roboto;
    background-color: gainsboro;
    height: 100%;
    margin: 0;
    display: flex;
    flex-flow: row wrap;
}

body > header {
    background-color: #e53c02;
    padding: 10px;
    width: 100%;
    order: 0;
}

body > nav {
    background-color: #39e502;
    padding: 10px;
    width: 20%;
    order: 0;
}

body > main {
    background-color: cornsilk;
    margin: 0;
    width: 80%;
    order: 1;
    display: flex;
    flex-flow: row wrap;
}

main > article {
    background-color: #02abe5;
    padding: 10px;
    width: 80%;
    order: 0;
}

main > aside {
    background-color: #ad02e5;
    padding: 10px;
    width: 20%;
    order: 1;
}

body > footer {
    background-color: #e53c02;
    padding: 10px;
    width: 100%;
    order: 3;
}

@media (max-width: 800px) {
    body > main {
        width: 100%;
    }
    body > nav {
        width: 100%;
        order: 0;
    }
    main > aside {
        width: 30%;
        order: 1;
    }
    main > article {
        width: 70%;
        order: 0;
    }
}

@media (max-width: 600px) {
    body > nav, body > main, main > article, main > aside {
        width: 100%;
    }
    main > aside {
        order: 1;
    }
}