* {
    box-sizing: border-box;
}

html,
body {
    padding: 0;
    margin: 0;
    font-family: verdana, arial, sans-serif;
}

body {
    font-size: 1.1em;
    padding: 1em;
    display: flex;
    flex-direction: column;
}

main {
    display: flex;
    flex-direction: column;
}

article {
    background-color: #546e7a;
    flex: 2 2 12em;
    padding: 1em;
}

nav,
aside {
    flex: 1;
}

nav {
    order: -1;
}

.tip-box {
    background: #e3f2fd;
    border-left: 4px solid #2196f3;
    padding: 20px;
    margin: 25px 0;
    border-radius: 0 8px 8px 0;
}

.tip-box strong {
    color: #0d47a1;
}


    footer {
        flex: 0 0 5em;
        background-color: #37474f;
    }

    @media screen and (min-width: 600px) {
        body {
            min-height: 100vh;
        }

        main {
            flex-direction: row;
            min-height: 100%;
            flex: 1 1 auto;
        }

        main>.img {
            flex-direction: row;
            min-width: 100%;
            min-height: 100%;
            flex: 1 1 auto;
        }
    }

    @media screen and (min-width: 480px) {
        body {
            min-height: 100vh;
        }

        main {
            flex-direction: row;
            min-height: 100%;
            flex: 1 1 auto;
        }

        main>.img {
            flex-direction: row;
            min-width: 100%;
            min-height: 100%;
            flex: 1 1 auto;
        }
    }