*{box-sizing: border-box;}
body{margin: 0;}
nav {
    background-color: lightgreen;
    overflow: hidden;
}

nav ul {
    list-style: none;
    text-align: center;
}

nav ul li {
    width: 33%;
    margin: 15px auto;
    float: left;
}

nav > a:nth-child(1){
    display: none; 
    color: orange;
}

@media screen and (max-width: 768px){

    nav > a:nth-child(1){
    display: block;
    font-size: 30px; 
    padding-left: 10px;
    text-decoration: none;
    background-color: #002a58;
    }
    
    
        *{box-sizing: border-box;}
    body{margin: 0;}
    nav {
        background-color: lightgreen;
        overflow: hidden;
    }
    
    nav ul {
        list-style: none;
        text-align: center;
        background-color: #002a58;
    }
    
    nav ul li {
        width: 100%;
        text-align: left;
        width: 90%;
        margin-left: 5%;
        margin-right: 5%;
        background-color: #002a58;
    }
    nav ul.menudicht {
        display: none; 
    }
    
    a{color: orange;}
}