#menu {
    height: 40px;
    background-color: #f00;
}

    #menu li {
        float: left;
        width: 16%;
        text-align: center;
        list-style: none;
        padding-top: 10px;
        font-size: 20px;
    }

        #menu li a {
            text-decoration: none;
        }

            #menu li a:hover {
                font-size: 22px;
            }

        #menu li:hover {
            background-color: #f00;
            height: 30px;
        }