* {
    box-sizing: border-box;
}

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

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

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

header > img {
    width: 20%;
    height: auto;
    float: right;
}

.clearright {
    clear: right;
}

nav {
    display: flex;
    justify-content: center;
}

nav > div {
    background-color: #f1f1f1;
    margin: 10px;
    padding: 10px 20px;
    font-size: 20px;
    text-align: center;
    flex: 1;
}

nav > div > a {
    color: steelblue;
    font-weight: bold;
    text-decoration: none;
}

nav > div > a:hover {
    color: royalblue;
    text-decoration: underline;
}

main {
    display: flex;
}

main > div {
    background-color: #f1f1f1;
    margin: 10px;
    padding: 10px;
    width: 100%;
}

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

footer p {
    text-align: center;
    color: black;
}

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

    header > img {
        width: 25%;
        height: auto;
        float: right;
    }
}

@media only screen and (max-width: 510px) {
    nav {
        flex-direction: column;
    }

    main {
        flex-direction: column;
    }

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

    main > div {
        margin: 5px;
    }

    header > img {
        width: 40%;
        height: auto;
        float: none;
        display: block;
        margin: auto;
    }
}