* {
    box-sizing: border-box
}

body {
    font-family: Arial, Helvetica, sans-serif;
    margin: 0
}

#wrapper {
    width: 80%;
    margin-left: auto;
    margin-right: auto;
    border: thin solid black
}

header {
    margin: 10px;
    padding: 10px;
    background-color: midnightblue;
    color: white
}

nav {
    display: flex;
    gap: 10px;
    margin: 10px
}

    nav > div {
        text-align: center;
        flex: 1;
        background: #eaeaea;
        padding: 10px;
        border: 1px solid #d9d9d9
    }

main {
    display: flex;
    gap: 10px;
    margin: 10px
}

    main > div {
        background: #f6f7f9;
        padding: 10px;
        border: 1px solid #ddd;
        flex: 1
    }

footer {
    background-color: midnightblue;
    margin: 10px;
    padding: 10px
}

    footer > p {
        text-align: center;
        color: white;
        margin: 0
    }

@media only screen and (max-width:1024px) {
    #wrapper {
        width: 100%;
        border: none
    }
}

@media only screen and (max-width:510px) {
    main {
        display: block;
        margin: 5px
    }

        main > div {
            margin: 5px
        }

    nav {
        display: block;
        margin: 5px
    }

        nav > div {
            width: auto;
            margin: 5px
        }
}