Data from MySQL not showing while building dynamic menu in PHP - php

Question

I'm building a dynamic menu using PHP and MySQL but results are not showing:
The website structure is built below:
<div id="container">
<ul class="nav">
<li>home</li>
<li>
destinations &triangledown;
<div id="subMenu">
<div class="nav-column">
Europe
</div>
<div class="nav-column" >
Africa
</div>
<div class="nav-column" >
Asia
</div>
<div class="nav-column">
Oceania
</div>
<div class="nav-column">
North America
</div>
<div class="nav-column">
South America
</div>
</div>
</li>
<li>about</li>
<li>contact</li>
</ul>
</div>
Then i have a continents DB and then another DB with countries, which connect to their respective continent.
So, in the subMenu div, i want to call each continent and then in each div cnt_submenu_, loop through a unordered list of 9 results and then show another with the same number of results and so on until all the countries with the same id reaches the end.
Here is what i'm trying to do with the PHP code below:
<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
?>
<div id="container">
<ul class="nav">
<li>home</li>
<li>destinations
<div id="subMenu">
<?php
$servername = "localhost:3306";
$username = "root";
$password = "";
$dbname = "site_comboios";
//Open DB connection
$mysqli = new mysqli($servername, $username, $password, $dbname);
//check connection
if($mysqli->connect_errno) {
echo 'Error connecting to database';
exit();
}
//show sub-menu
$query = "SELECT * FROM continentes ORDER BY id";
$result = mysqli_query($mysqli, $query);
$div = 0;
while ($row = mysqli_fetch_assoc($result)) {
$país = $row['continente'];
echo "<div class='nav-column'><a href='#' class='continente' data-id='cnt_submenu'>" .($país). "</a></div> "; </div> ";
}
?>
</div>
</li>
<li>about</li>
<li>contact</li>
</ul>
</div>
<div id="cnt_submenu_" class="submenu_continente active">
<?php
//retrieve european countries from DB and open <ul> with 9 results
$conn = mysqli_connect("localhost:3306","root","","site_comboios");
$sql_countries = "SELECT * FROM countries ORDER BY id WHERE id_continentes = 1" ;
$res_countries = mysqli_query($conn, $sql_countries);
if($res_countries > 0) {
while ($row_countries = mysqli_fetch_assoc($res_countries)) {
$país = $row_countries['id_continente'];
echo "<ul><li><a href='#'>". $país ."";
}
} else if ($res_countries == 9) {
echo '</li></ul>';
}
?>
<span class="close">x</span>
</div>
Thanks for pointing me out in the right direction.
Edited I'm trying to show through 9 results onto a , close it and open another with 9 results until the end of the countries with id = 1.
Added the jquery to open each continent div below but i'm not doing it right:
//Open and close each div with country list
$('.continente').hover(function(){
menuHide('submenu_continente' . $(this).data("id") );
$('#cnt_submenu_' . $(this).data("id") ).show();
},function(){
$('#cnt_submenu_' . $(this).data("id")).mouseleave( function() {
$(this).hide();
});
});