style.css

body
{
    background-color: #f7efeb;
    padding: 1.25em; /* 20 */
}

#nav
{
    width: 60em; /* 1000 */
    font-family: 'Open Sans', sans-serif;
    font-weight: 400;
    position: relative;
    top: 25%;
    left: 50%;
    margin-left: -30em; /* 30 480 */
}

    #nav > a
    {
        display: none;
    }

    #nav li
    {
        position: relative;
    }
        #nav li a
        {
            color: #fff;
            display: block;
        }
        #nav li a:active
        {
            background-color: #c00 !important;
        }

    #nav span:after
    {
        width: 0;
        height: 0;
        border: 0.313em solid transparent; /* 5 */
        border-bottom: none;
        border-top-color: #efa585;
        content: '';
        vertical-align: middle;
        display: inline-block;
        position: relative;
        right: -0.313em; /* 5 */
    }

    /* first level */

    #nav > ul
    {
        height: 3.75em; /* 60 */
        background-color: #e15a1f;
    }
        #nav > ul > li
        {
            width: 25%;
            height: 100%;
            float: left;
        }
            #nav > ul > li > a
            {
                height: 100%;
                font-size: 1.5em; /* 24 */
                line-height: 2.5em; /* 60 (24) */
                text-align: center;
            }
                #nav > ul > li:not( :last-child ) > a
                {
                    border-right: 1px solid #cc470d;
                }
                #nav > ul > li:hover > a,
                #nav > ul:not( :hover ) > li.active > a
                {
                    background-color: #cc470d;
                }


        /* second level */

        #nav li ul
        {
            background-color: #cc470d;
            display: none;
            position: absolute;
            top: 100%;
        }
            #nav li:hover ul
            {
                display: block;
                left: 0;
                right: 0;
            }
                #nav li:not( :first-child ):hover ul
                {
                    left: -1px;
                }
                #nav li ul a
                {
                    font-size: 1.25em; /* 20 */
                    border-top: 1px solid #e15a1f;
                    padding: 0.75em; /* 15 (20) */
                }
                    #nav li ul li a:hover,
                    #nav li ul:not( :hover ) li.active a
                    {
                        background-color: #e15a1f;
                    }


@media only screen and ( max-width: 62.5em ) /* 1000 */
{
    #nav
    {
        width: 100%;
        position: static;
        margin: 0;
    }
}

@media only screen and ( max-width: 40em ) /* 640 */
{
    html
    {
        font-size: 75%; /* 12 */
    }

    #nav
    {
        position: relative;
        top: auto;
        left: auto;
    }
        #nav > a
        {
            width: 3.125em; /* 50 */
            height: 3.125em; /* 50 */
            text-align: left;
            text-indent: -9999px;
            background-color: #e15a1f;
            position: relative;
        }
            #nav > a:before,
            #nav > a:after
            {
                position: absolute;
                border: 2px solid #fff;
                top: 35%;
                left: 25%;
                right: 25%;
                content: '';
            }
            #nav > a:after
            {
                top: 60%;
            }

        #nav:not( :target ) > a:first-of-type,
        #nav:target > a:last-of-type
        {
            display: block;
        }


    /* first level */

    #nav > ul
    {
        height: auto;
        display: none;
        position: absolute;
        left: 0;
        right: 0;
    }
        #nav:target > ul
        {
            display: block;
        }
        #nav > ul > li
        {
            width: 100%;
            float: none;
        }
            #nav > ul > li > a
            {
                height: auto;
                text-align: left;
                padding: 0 0.833em; /* 20 (24) */
            }
                #nav > ul > li:not( :last-child ) > a
                {
                    border-right: none;
                    border-bottom: 1px solid #cc470d;
                }


        /* second level */

        #nav li ul
        {
            position: static;
            padding: 1.25em; /* 20 */
            padding-top: 0;
        }
}