body {
    background-color: #222222;
    color: #ffffff;
    font-family: Helvetica, Verdana, sans-serif;
    margin: 0;
}

nav ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background-color: #4a7e5d;
    border-bottom: solid #2a5e3d 2px;
}

nav ul li {
    float: left;
}

nav ul li a {
    font-weight: bold;
    display: block;
    color: #ffffff;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
}

nav ul li a:hover {
    color: #efefef;
    background-color: #3a6e4d;
}

main {
    width: 95%;
    float: right;
}

section.resumo, section.desenhos {
    margin-top: 20px;
}

section.resumo h1, section.resumo h2 {
    margin-left: 16px;
}

section.resumo h1 {
    font-size: 24px;
}

section.resumo h2 {
    font-size: 18px;
}

section.resumo h3 {
    font-size: 16px;
}

section.resumo {
    width: 60%;
    float: left;
    margin-bottom: 60px;
}

section.resumo div, section.desenhos div {
    width: 90%;
    margin: auto;
}

section.desenhos {
    width: 40%;
    float: left;
}

section.desenhos div {
    width: 50%;
    padding-top: 50%;
    margin: 30px auto;
    background-repeat: no-repeat;
    background-size: contain;
}

section.desenhos #retangular {
    background-image: url('retangular.gif');
}

section.desenhos #grade {
    background-image: url('grade-y.gif');
}


@media screen and (max-width: 800px) {
    main {
        float: none;
        width: 100%;
    }

    section.resumo, section.desenhos {
        float: none;
        width: 100%;
    }

    section.resumo {
        margin-top: 40px;
    }

    nav ul {
        border: none;
    }

    nav ul li {
        float: none;
        border-bottom: solid #1a6e4d 2px;
    }
}