html {
    height: 100%;
}

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

body {
    font-family: Roboto;
    background-color: gainsboro;
    height: 100%;
    border: 1px solid black;
    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: 100%;
    order: 1;
}

body>article {
    background-color: #02abe5;
    padding: 10px;
    width: 80%;
    order: 2;
}

body>aside {
    background-color: #ad02e5;
    padding: 10px;
    width: 20%;
    order: 3;
}

body>footer {
    background-color: #e53c02;
    padding: 10px;
    width: 100%;
    order: 4;
}

@media (max-width: 800px) {
    body>header, body>aside, body>footer {
        width: 100%;
    }
    body>nav {
        width: 30%;
        order: 2;
    }
    body>article {
        width: 70%;
    }
}

@media (max-width: 600px) {
    body>header, body>nav, body>article, body>aside, body>footer {
        width: 100%;
    }
    body>aside {
        order: 3;
    }
}