.topnav {
    position: fixed;
    width: 100%;
    overflow: hidden;
    background-color:  #339933;
    box-shadow: 0 5px 8px 0 rgba(0,0,0,0.2);
}

.topnav a {
    float: left;
    color: #f2f2f2;
    text-align: center;
    padding: 10px 16px;
    text-decoration: none;
    font-size: 20px;
}

.topnav a:hover {
    background-color: #ddd;
    color: black;
}

.topnav a.active {
    font-weight: bold;
}