Responsive Navbar with Dropdown don't show dropdown menu - html

Question

I have to put a respnsive menu with submenus.
I found this lesson : https://www.w3schools.com/howto/howto_js_responsive_navbar_dropdown.asp
The menu itself comes out, but when I click the "Dropdown" button, the submenus are not displayed at all.I tried to change some code but nothing get.
How can I fix this or where to look for the problem?
Thanks in advance!
function myFunction() {
var x = document.getElementById("myTopnav");
if (x.className === "topnav") {
x.className += " responsive";
} else {
x.className = "topnav";
}
}
#navbaronder {
background-color: #dddddd;
margin: 155px 0px 0px 0px; /* viso4ina na drop down menuto*/
transition: 0.4s;
position: fixed;
width: 100%;
top: 0;
z-index: 500;
}
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css"/>
<style>
body {margin:0;font-family:Arial}
.topnav {
overflow: hidden;
background-color: #333;
}
.topnav a {
float: right;
display: block;
color: #f2f2f2;
text-align: center;
padding: 14px 16px;
text-decoration: none;
font-size: 17px;
}
.active {
background-color: #4CAF50;
color: white;
}
.topnav .icon {
display: none;
}
.dropdown {
float: right;
overflow: hidden;
}
.dropdown .dropbtn {
font-size: 17px;
border: none;
outline: none;
color: white;
padding: 14px 16px;
background-color: inherit;
font-family: inherit;
margin: 0;
}
.dropdown-content {
display: none;
position: absolute;
background-color: #f9f9f9;
min-width: 160px;
box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
z-index: 1;
}
.dropdown-content a {
float: none;
color: black;
padding: 12px 16px;
text-decoration: none;
display: block;
text-align: left;
}
.topnav a:hover, .dropdown:hover .dropbtn {
background-color: #555;
color: white;
}
.dropdown-content a:hover {
background-color: #ddd;
color: black;
}
.dropdown:hover .dropdown-content {
display: block;
}
#media screen and (max-width: 600px) {
.topnav a:not(:first-child), .dropdown .dropbtn {
display: none;
}
.topnav a.icon {
float: right;
display: block;
}
}
#media screen and (max-width: 600px) {
.topnav.responsive {position: relative;}
.topnav.responsive .icon {
position: absolute;
right: 0;
top: 0;
}
.topnav.responsive a {
float: none;
display: block;
text-align: left;
}
.topnav.responsive .dropdown {float: none;}
.topnav.responsive .dropdown-content {position: relative;}
.topnav.responsive .dropdown .dropbtn {
display: block;
width: 100%;
text-align: left;
}
}
</style>
<div id="navbaronder">
<div class="topnav" id="myTopnav">
Home
News
Contact
<div class="dropdown">
<button class="dropbtn">Dropdown
<i class="fa fa-caret-down"></i>
</button>
<div class="dropdown-content">
Link 1
Link 2
Link 3
</div>
</div>
About
☰
</div>
</div>